diff --git a/fmt/format.cc b/fmt/format.cc
index 499e8382..3e2a6eec 100644
--- a/fmt/format.cc
+++ b/fmt/format.cc
@@ -443,8 +443,7 @@ template <typename Char>
 void printf(BasicWriter<Char> &w, BasicCStringRef<Char> format,
             format_args args);
 
-FMT_FUNC int vfprintf(std::FILE *f, CStringRef format,
-                      basic_format_args<printf_context<char>> args) {
+FMT_FUNC int vfprintf(std::FILE *f, CStringRef format, printf_args args) {
   MemoryWriter w;
   printf(w, format, args);
   std::size_t size = w.size();
@@ -475,7 +474,7 @@ template int internal::CharTraits<char>::format_float(
 
 template void internal::FixedBuffer<wchar_t>::grow(std::size_t);
 
-template void internal::ArgMap<wchar_t>::init(const format_args &args);
+template void internal::ArgMap<wchar_t>::init(const wformat_args &args);
 
 template void printf_context<wchar_t>::format(WWriter &writer);
 
diff --git a/fmt/format.h b/fmt/format.h
index e03c66aa..ed706466 100644
--- a/fmt/format.h
+++ b/fmt/format.h
@@ -414,6 +414,8 @@ class BasicStringRef {
   std::size_t size_;
 
  public:
+  BasicStringRef() : data_(0), size_(0) {}
+
   /** Constructs a string reference object from a C string and a size. */
   BasicStringRef(const Char *s, std::size_t size) : data_(s), size_(size) {}
 
@@ -1027,16 +1029,102 @@ struct Value {
     CSTRING, STRING, WSTRING, POINTER, CUSTOM
   };
 };
+
+template <typename Char>
+class ArgMap;
 }  // namespace internal
 
+template <typename Context, typename Char>
+class basic_format_args;
+
 // A formatting argument. It is a trivially copyable/constructible type to
 // allow storage in internal::MemoryBuffer.
-struct format_arg : internal::Value {
-  Type type;
+template <typename Char>
+class basic_format_arg : public internal::Value {
+ protected:
+  Type type_;
 
-  explicit operator bool() const noexcept { return type != NONE; }
+  template <typename Visitor, typename CharType>
+  friend typename std::result_of<Visitor(int)>::type
+    visit(Visitor &&vis, basic_format_arg<CharType> arg);
+
+  template <typename Context, typename CharType>
+  friend class basic_format_args;
+
+  template <typename CharType>
+  friend class internal::ArgMap;
+
+  void check_type() const {
+    FMT_ASSERT(type_ > NAMED_ARG, "invalid argument type");
+  }
+
+ public:
+  explicit operator bool() const noexcept { return type_ != NONE; }
+
+  bool is_integral() const {
+    check_type();
+    return type_ <= LAST_INTEGER_TYPE;
+  }
+
+  bool is_numeric() const {
+    check_type();
+    return type_ <= LAST_NUMERIC_TYPE;
+  }
+
+  bool is_pointer() const {
+    check_type();
+    return type_ == POINTER;
+  }
 };
 
+typedef basic_format_arg<char> format_arg;
+typedef basic_format_arg<wchar_t> wformat_arg;
+
+/**
+  \rst
+  Visits an argument dispatching to the appropriate visit method based on
+  the argument type. For example, if the argument type is ``double`` then
+  ``vis(value)`` will be called with the value of type ``double``.
+  \endrst
+ */
+template <typename Visitor, typename Char>
+typename std::result_of<Visitor(int)>::type
+    visit(Visitor &&vis, basic_format_arg<Char> arg) {
+  switch (arg.type_) {
+  case format_arg::NONE:
+  case format_arg::NAMED_ARG:
+    FMT_ASSERT(false, "invalid argument type");
+    break;
+  case format_arg::INT:
+    return vis(arg.int_value);
+  case format_arg::UINT:
+    return vis(arg.uint_value);
+  case format_arg::LONG_LONG:
+    return vis(arg.long_long_value);
+  case format_arg::ULONG_LONG:
+    return vis(arg.ulong_long_value);
+  case format_arg::BOOL:
+    return vis(arg.int_value != 0);
+  case format_arg::CHAR:
+    return vis(static_cast<Char>(arg.int_value));
+  case format_arg::DOUBLE:
+    return vis(arg.double_value);
+  case format_arg::LONG_DOUBLE:
+    return vis(arg.long_double_value);
+  case format_arg::CSTRING:
+    return vis(arg.string.value);
+  case format_arg::STRING:
+    return vis(arg.string);
+  case format_arg::WSTRING:
+    return vis(arg.wstring);
+  case format_arg::POINTER:
+    return vis(arg.pointer);
+  case format_arg::CUSTOM:
+    return vis(arg.custom);
+  }
+  return typename std::result_of<Visitor(int)>::type();
+}
+
 namespace internal {
 
 template <typename Char>
@@ -1251,7 +1339,7 @@ constexpr Type type() { return gettype<typename std::decay<T>::type>(); }
 
 // Makes a format_arg object from any type.
 template <typename Context>
-class MakeValue : public format_arg {
+class MakeValue : public basic_format_arg<typename Context::char_type> {
  public:
   typedef typename Context::char_type Char;
 
@@ -1279,13 +1367,13 @@ class MakeValue : public format_arg {
   MakeValue(typename WCharHelper<WStringRef, Char>::Unsupported);
 
   void set_string(StringRef str) {
-    string.value = str.data();
-    string.size = str.size();
+    this->string.value = str.data();
+    this->string.size = str.size();
   }
 
   void set_string(WStringRef str) {
-    wstring.value = str.data();
-    wstring.size = str.size();
+    this->wstring.value = str.data();
+    this->wstring.size = str.size();
   }
 
   // Formats an argument of a custom type, such as a user-defined class.
@@ -1302,8 +1390,8 @@ class MakeValue : public format_arg {
 
 #define FMT_MAKE_VALUE_(Type, field, TYPE, rhs) \
   MakeValue(Type value) { \
-    static_assert(internal::type<Type>() == TYPE, "invalid type"); \
-    field = rhs; \
+    static_assert(internal::type<Type>() == MakeValue::TYPE, "invalid type"); \
+    this->field = rhs; \
   }
 
 #define FMT_MAKE_VALUE(Type, field, TYPE) \
@@ -1319,16 +1407,16 @@ class MakeValue : public format_arg {
     // To minimize the number of types we need to deal with, long is
     // translated either to int or to long long depending on its size.
     if (const_check(sizeof(long) == sizeof(int)))
-      int_value = static_cast<int>(value);
+      this->int_value = static_cast<int>(value);
     else
-      long_long_value = value;
+      this->long_long_value = value;
   }
 
   MakeValue(unsigned long value) {
     if (const_check(sizeof(unsigned long) == sizeof(unsigned)))
-      uint_value = static_cast<unsigned>(value);
+      this->uint_value = static_cast<unsigned>(value);
     else
-      ulong_long_value = value;
+      this->ulong_long_value = value;
   }
 
   FMT_MAKE_VALUE(LongLong, long_long_value, LONG_LONG)
@@ -1343,14 +1431,14 @@ class MakeValue : public format_arg {
 #if !defined(_MSC_VER) || defined(_NATIVE_WCHAR_T_DEFINED)
   typedef typename WCharHelper<wchar_t, Char>::Supported WChar;
   MakeValue(WChar value) {
-    static_assert(internal::type<WChar>() == CHAR, "invalid type");
-    int_value = value;
+    static_assert(internal::type<WChar>() == MakeValue::CHAR, "invalid type");
+    this->int_value = value;
   }
 #endif
 
 #define FMT_MAKE_STR_VALUE(Type, TYPE) \
   MakeValue(Type value) { \
-    static_assert(internal::type<Type>() == TYPE, "invalid type"); \
+    static_assert(internal::type<Type>() == MakeValue::TYPE, "invalid type"); \
     set_string(value); \
   }
 
@@ -1366,7 +1454,7 @@ class MakeValue : public format_arg {
 
 #define FMT_MAKE_WSTR_VALUE(Type, TYPE) \
   MakeValue(typename WCharHelper<Type, Char>::Supported value) { \
-  static_assert(internal::type<Type>() == TYPE, "invalid type"); \
+  static_assert(internal::type<Type>() == MakeValue::TYPE, "invalid type"); \
     set_string(value); \
   }
 
@@ -1382,49 +1470,51 @@ class MakeValue : public format_arg {
   MakeValue(const T &value,
             typename EnableIf<Not<
               ConvertToInt<T>::value>::value, int>::type = 0) {
-    static_assert(internal::type<T>() == CUSTOM, "invalid type");
-    custom.value = &value;
-    custom.format = &format_custom_arg<T>;
+    static_assert(internal::type<T>() == MakeValue::CUSTOM, "invalid type");
+    this->custom.value = &value;
+    this->custom.format = &format_custom_arg<T>;
   }
 
   template <typename T>
   MakeValue(const T &value,
             typename EnableIf<ConvertToInt<T>::value, int>::type = 0) {
-    static_assert(internal::type<T>() == INT, "invalid type");
-    int_value = value;
+    static_assert(internal::type<T>() == MakeValue::INT, "invalid type");
+    this->int_value = value;
   }
 
   // Additional template param `Char_` is needed here because make_type always
   // uses char.
   template <typename Char_>
   MakeValue(const NamedArg<Char_> &value) {
-    static_assert(internal::type<const NamedArg<Char_> &>() == NAMED_ARG,
-                  "invalid type");
-    pointer = &value;
+    static_assert(
+      internal::type<const NamedArg<Char_> &>() == MakeValue::NAMED_ARG,
+      "invalid type");
+    this->pointer = &value;
   }
 };
 
 template <typename Context>
-class MakeArg : public format_arg {
+  class MakeArg : public basic_format_arg<typename Context::char_type> {
 public:
   MakeArg() {
-    type = format_arg::NONE;
+    this->type_ = format_arg::NONE;
   }
 
   template <typename T>
   MakeArg(const T &value)
-  : format_arg(MakeValue<Context>(value)) {
-    type = internal::type<T>();
+  : basic_format_arg<typename Context::char_type>(MakeValue<Context>(value)) {
+    this->type_ = internal::type<T>();
   }
 };
 
 template <typename Char>
-struct NamedArg : format_arg {
+struct NamedArg : basic_format_arg<Char> {
   BasicStringRef<Char> name;
 
   template <typename T>
   NamedArg(BasicStringRef<Char> argname, const T &value)
-  : format_arg(MakeArg< basic_format_context<Char> >(value)), name(argname) {}
+  : basic_format_arg<Char>(MakeArg< basic_format_context<Char> >(value)),
+    name(argname) {}
 };
 
 class RuntimeError : public std::runtime_error {
@@ -1433,9 +1523,6 @@ class RuntimeError : public std::runtime_error {
   ~RuntimeError() throw();
 };
 
-template <typename Char>
-class ArgMap;
-
 template <typename Arg, typename... Args>
 constexpr uint64_t make_type() {
   return type<Arg>() | (make_type<Args...>() << 4);
@@ -1482,8 +1569,12 @@ inline format_arg_store<format_context, Args...>
 }
 
 /** Formatting arguments. */
-template <typename Context>
+template <typename Context, typename Char>
 class basic_format_args {
+ public:
+  typedef unsigned size_type;
+  typedef basic_format_arg<Char> format_arg;
+
  private:
   // To reduce compiled code size per formatting function call, types of first
   // MAX_PACKED_ARGS arguments are passed in the types_ field.
@@ -1498,21 +1589,43 @@ class basic_format_args {
     const format_arg *args_;
   };
 
-  format_arg::Type type(unsigned index) const {
+  typename format_arg::Type type(unsigned index) const {
     unsigned shift = index * 4;
     uint64_t mask = 0xf;
-    return static_cast<format_arg::Type>((types_ & (mask << shift)) >> shift);
+    return static_cast<typename format_arg::Type>(
+      (types_ & (mask << shift)) >> shift);
   }
 
-  template <typename Char>
-  friend class internal::ArgMap;
+  friend class internal::ArgMap<Char>;
 
   void set_data(const internal::Value *values) { values_ = values; }
   void set_data(const format_arg *args) { args_ = args; }
 
- public:
-  typedef unsigned size_type;
+  format_arg get(size_type index) const {
+    format_arg arg;
+    bool use_values = type(internal::MAX_PACKED_ARGS - 1) == format_arg::NONE;
+    if (index < internal::MAX_PACKED_ARGS) {
+      typename format_arg::Type arg_type = type(index);
+      internal::Value &val = arg;
+      if (arg_type != format_arg::NONE)
+        val = use_values ? values_[index] : args_[index];
+      arg.type_ = arg_type;
+      return arg;
+    }
+    if (use_values) {
+      // The index is greater than the number of arguments that can be stored
+      // in values, so return a "none" argument.
+      arg.type_ = format_arg::NONE;
+      return arg;
+    }
+    for (unsigned i = internal::MAX_PACKED_ARGS; i <= index; ++i) {
+      if (args_[i].type_ == format_arg::NONE)
+        return args_[i];
+    }
+    return args_[index];
+  }
 
+ public:
   basic_format_args() : types_(0) {}
 
   template <typename... Args>
@@ -1523,77 +1636,14 @@ class basic_format_args {
 
   /** Returns the argument at specified index. */
   format_arg operator[](size_type index) const {
-    format_arg arg;
-    bool use_values = type(internal::MAX_PACKED_ARGS - 1) == format_arg::NONE;
-    if (index < internal::MAX_PACKED_ARGS) {
-      format_arg::Type arg_type = type(index);
-      internal::Value &val = arg;
-      if (arg_type != format_arg::NONE)
-        val = use_values ? values_[index] : args_[index];
-      arg.type = arg_type;
-      return arg;
-    }
-    if (use_values) {
-      // The index is greater than the number of arguments that can be stored
-      // in values, so return a "none" argument.
-      arg.type = format_arg::NONE;
-      return arg;
-    }
-    for (unsigned i = internal::MAX_PACKED_ARGS; i <= index; ++i) {
-      if (args_[i].type == format_arg::NONE)
-        return args_[i];
-    }
-    return args_[index];
+    format_arg arg = get(index);
+    return arg.type_ == format_arg::NAMED_ARG ?
+      *static_cast<const format_arg*>(arg.pointer) : arg;
   }
 };
 
-typedef basic_format_args<basic_format_context<char>> format_args;
-typedef basic_format_args<basic_format_context<wchar_t>> wformat_args;
-
-/**
-  \rst
-  Visits an argument dispatching to the appropriate visit method based on
-  the argument type. For example, if the argument type is ``double`` then
-  ``vis(value)`` will be called with the value of type ``double``.
-  \endrst
- */
-template <typename Visitor>
-typename std::result_of<Visitor(int)>::type visit(Visitor &&vis,
-                                                  format_arg arg) {
-  switch (arg.type) {
-  case format_arg::NONE:
-  case format_arg::NAMED_ARG:
-    FMT_ASSERT(false, "invalid argument type");
-    break;
-  case format_arg::INT:
-    return vis(arg.int_value);
-  case format_arg::UINT:
-    return vis(arg.uint_value);
-  case format_arg::LONG_LONG:
-    return vis(arg.long_long_value);
-  case format_arg::ULONG_LONG:
-    return vis(arg.ulong_long_value);
-  case format_arg::BOOL:
-    return vis(arg.int_value != 0);
-  case format_arg::CHAR:
-    return vis(static_cast<wchar_t>(arg.int_value));
-  case format_arg::DOUBLE:
-    return vis(arg.double_value);
-  case format_arg::LONG_DOUBLE:
-    return vis(arg.long_double_value);
-  case format_arg::CSTRING:
-    return vis(arg.string.value);
-  case format_arg::STRING:
-    return vis(arg.string);
-  case format_arg::WSTRING:
-    return vis(arg.wstring);
-  case format_arg::POINTER:
-    return vis(arg.pointer);
-  case format_arg::CUSTOM:
-    return vis(arg.custom);
-  }
-  return typename std::result_of<Visitor(int)>::type();
-}
+typedef basic_format_args<basic_format_context<char>, char> format_args;
+typedef basic_format_args<basic_format_context<wchar_t>, wchar_t> wformat_args;
 
 enum Alignment {
   ALIGN_DEFAULT, ALIGN_LEFT, ALIGN_RIGHT, ALIGN_CENTER, ALIGN_NUMERIC
@@ -1822,16 +1872,17 @@ template <typename Char>
 class ArgMap {
  private:
   typedef std::vector<
-    std::pair<fmt::BasicStringRef<Char>, format_arg> > MapType;
+    std::pair<fmt::BasicStringRef<Char>, basic_format_arg<Char> > > MapType;
   typedef typename MapType::value_type Pair;
 
   MapType map_;
 
  public:
-  template <typename Formatter>
-  void init(const basic_format_args<Formatter> &args);
+  template <typename Context>
+  void init(const basic_format_args<Context, Char> &args);
 
-  const format_arg *find(const fmt::BasicStringRef<Char> &name) const {
+  const basic_format_arg<Char>
+      *find(const fmt::BasicStringRef<Char> &name) const {
     // The list is unsorted, so just return the first matching name.
     for (typename MapType::const_iterator it = map_.begin(), end = map_.end();
          it != end; ++it) {
@@ -1843,8 +1894,8 @@ class ArgMap {
 };
 
 template <typename Char>
-template <typename Formatter>
-void ArgMap<Char>::init(const basic_format_args<Formatter> &args) {
+template <typename Context>
+void ArgMap<Char>::init(const basic_format_args<Context, Char> &args) {
   if (!map_.empty())
     return;
   typedef internal::NamedArg<Char> NamedArg;
@@ -1874,8 +1925,8 @@ void ArgMap<Char>::init(const basic_format_args<Formatter> &args) {
       map_.push_back(Pair(named_arg->name, *named_arg));
     }
   }
-  for (unsigned i = MAX_PACKED_ARGS;/*nothing*/; ++i) {
-    switch (args.args_[i].type) {
+  for (unsigned i = MAX_PACKED_ARGS; ; ++i) {
+    switch (args.args_[i].type_) {
       case format_arg::NONE:
         return;
       case format_arg::NAMED_ARG:
@@ -1955,7 +2006,7 @@ class ArgFormatterBase {
     write(value);
   }
 
-  void operator()(wchar_t value) {
+  void operator()(Char value) {
     if (spec_.type_ && spec_.type_ != 'c') {
       spec_.flags_ |= CHAR_FLAG;
       writer_.write_int(value, spec_);
@@ -2016,29 +2067,24 @@ template <typename Char, typename Context>
 class format_context_base {
  private:
   const Char *ptr_;
-  basic_format_args<Context> args_;
+  basic_format_args<Context, Char> args_;
   int next_arg_index_;
 
  protected:
-  format_context_base(const Char *format_str, basic_format_args<Context> args)
+  typedef basic_format_arg<Char> format_arg;
+
+  format_context_base(const Char *format_str,
+                      basic_format_args<Context, Char> args)
   : ptr_(format_str), args_(args), next_arg_index_(0) {}
   ~format_context_base() {}
 
-  basic_format_args<Context> args() const { return args_; }
+  basic_format_args<Context, Char> args() const { return args_; }
 
   // Returns the argument with specified index.
   format_arg do_get_arg(unsigned arg_index, const char *&error) {
     format_arg arg = args_[arg_index];
-    switch (arg.type) {
-      case format_arg::NONE:
-        error = "argument index out of range";
-        break;
-      case format_arg::NAMED_ARG:
-        arg = *static_cast<const format_arg*>(arg.pointer);
-        break;
-      default:
-        /*nothing*/;
-    }
+    if (!arg)
+      error = "argument index out of range";
     return arg;
   }
 
@@ -2107,13 +2153,14 @@ class basic_format_context :
 
   FMT_DISALLOW_COPY_AND_ASSIGN(basic_format_context);
 
-  typedef internal::format_context_base<Char, basic_format_context> Base;
+  typedef internal::format_context_base<Char, basic_format_context<Char>> Base;
 
+  using typename Base::format_arg;
   using Base::get_arg;
 
   // Checks if manual indexing is used and returns the argument with
   // specified name.
-  format_arg get_arg(BasicStringRef<Char> name, const char *&error);
+  basic_format_arg<Char> get_arg(BasicStringRef<Char> name, const char *&error);
 
  public:
   /** The character type for the output. */
@@ -2126,11 +2173,11 @@ class basic_format_context :
    \endrst
    */
   basic_format_context(const Char *format_str,
-                       basic_format_args<basic_format_context> args)
+                       basic_format_args<basic_format_context, Char> args)
   : Base(format_str, args) {}
 
   // Parses argument id and returns corresponding argument.
-  format_arg parse_arg_id();
+  basic_format_arg<Char> parse_arg_id();
 
   using Base::ptr;
 };
@@ -2364,7 +2411,7 @@ class BasicWriter {
   }
 
   void vwrite(BasicCStringRef<Char> format,
-              basic_format_args<basic_format_context<Char>> args);
+              basic_format_args<basic_format_context<Char>, Char> args);
   /**
     \rst
     Writes formatted data.
@@ -3281,45 +3328,121 @@ unsigned parse_nonnegative_int(const Char *&s) {
   return value;
 }
 
-inline void require_numeric_argument(const format_arg &arg, char spec) {
-  if (arg.type > format_arg::LAST_NUMERIC_TYPE) {
-    std::string message =
-        fmt::format("format specifier '{}' requires numeric argument", spec);
-    FMT_THROW(fmt::format_error(message));
+template <typename Char>
+inline void require_numeric_argument(
+    const basic_format_arg<Char> &arg, char spec) {
+  if (!arg.is_numeric()) {
+    FMT_THROW(fmt::format_error(
+        fmt::format("format specifier '{}' requires numeric argument", spec)));
   }
 }
 
+struct IsUnsigned {
+  template <typename T>
+  typename std::enable_if<std::is_unsigned<T>::value, bool>::type
+      operator()(T value) {
+    return true;
+  }
+
+  template <typename T>
+  typename std::enable_if<!std::is_unsigned<T>::value, bool>::type
+      operator()(T value) {
+    return false;
+  }
+};
+
 template <typename Char>
-void check_sign(const Char *&s, const format_arg &arg) {
+void check_sign(const Char *&s, const basic_format_arg<Char> &arg) {
   char sign = static_cast<char>(*s);
   require_numeric_argument(arg, sign);
-  if (arg.type == format_arg::UINT || arg.type == format_arg::ULONG_LONG) {
+  if (visit(IsUnsigned(), arg)) {
     FMT_THROW(format_error(fmt::format(
       "format specifier '{}' requires signed argument", sign)));
   }
   ++s;
 }
+
+template <typename Char, typename Context>
+class CustomFormatter {
+ private:
+  BasicWriter<Char> &writer_;
+  Context &ctx_;
+
+ public:
+  CustomFormatter(BasicWriter<Char> &writer, Context &ctx)
+  : writer_(writer), ctx_(ctx) {}
+
+  bool operator()(format_arg::CustomValue custom) {
+    custom.format(&writer_, custom.value, &ctx_);
+    return true;
+  }
+
+  template <typename T>
+  bool operator()(T) { return false; }
+};
+
+template <typename T>
+struct IsInteger {
+  enum {
+    value = std::is_integral<T>::value && !std::is_same<T, bool>::value &&
+            !std::is_same<T, char>::value && !std::is_same<T, wchar_t>::value
+  };
+};
+
+struct WidthHandler {
+  template <typename T>
+  typename std::enable_if<IsInteger<T>::value, ULongLong>::type
+      operator()(T value) {
+    if (is_negative(value))
+      FMT_THROW(format_error("negative width"));
+    return value;
+  }
+
+  template <typename T>
+  typename std::enable_if<!IsInteger<T>::value, ULongLong>::type
+      operator()(T value) {
+    FMT_THROW(format_error("width is not integer"));
+    return 0;
+  }
+};
+
+struct PrecisionHandler {
+  template <typename T>
+  typename std::enable_if<IsInteger<T>::value, ULongLong>::type
+      operator()(T value) {
+    if (is_negative(value))
+      FMT_THROW(format_error("negative precision"));
+    return value;
+  }
+
+  template <typename T>
+  typename std::enable_if<!IsInteger<T>::value, ULongLong>::type
+      operator()(T value) {
+    FMT_THROW(format_error("precision is not integer"));
+    return 0;
+  }
+};
 }  // namespace internal
 
 template <typename Char>
-inline format_arg basic_format_context<Char>::get_arg(
+inline basic_format_arg<Char> basic_format_context<Char>::get_arg(
     BasicStringRef<Char> name, const char *&error) {
   if (this->check_no_auto_index(error)) {
     map_.init(this->args());
-    const format_arg *arg = map_.find(name);
+    const basic_format_arg<Char> *arg = map_.find(name);
     if (arg)
       return *arg;
     error = "argument not found";
   }
-  return format_arg();
+  return basic_format_arg<Char>();
 }
 
 template <typename Char>
-inline format_arg basic_format_context<Char>::parse_arg_id() {
+inline basic_format_arg<Char> basic_format_context<Char>::parse_arg_id() {
   const Char *&s = this->ptr();
   if (!internal::is_name_start(*s)) {
     const char *error = 0;
-    format_arg arg = *s < '0' || *s > '9' ?
+    basic_format_arg<Char> arg = *s < '0' || *s > '9' ?
       this->next_arg(error) : get_arg(internal::parse_nonnegative_int(s), error);
     if (error) {
       FMT_THROW(format_error(
@@ -3333,7 +3456,8 @@ inline format_arg basic_format_context<Char>::parse_arg_id() {
     c = *++s;
   } while (internal::is_name_start(c) || ('0' <= c && c <= '9'));
   const char *error = 0;
-  format_arg arg = get_arg(BasicStringRef<Char>(start, s - start), error);
+  basic_format_arg<Char> arg =
+    get_arg(BasicStringRef<Char>(start, s - start), error);
   if (error)
     FMT_THROW(format_error(error));
   return arg;
@@ -3341,15 +3465,13 @@ inline format_arg basic_format_context<Char>::parse_arg_id() {
 
 // Formats a single argument.
 template <typename ArgFormatter, typename Char, typename Context>
-void do_format_arg(BasicWriter<Char> &writer, const format_arg &arg,
+void do_format_arg(BasicWriter<Char> &writer, const basic_format_arg<Char> &arg,
                    Context &ctx) {
   const Char *&s = ctx.ptr();
   FormatSpec spec;
   if (*s == ':') {
-    if (arg.type == format_arg::CUSTOM) {
-      arg.custom.format(&writer, arg.custom.value, &ctx);
+    if (visit(internal::CustomFormatter<Char, Context>(writer, ctx), arg))
       return;
-    }
     ++s;
     // Parse fill and alignment.
     if (Char c = *s) {
@@ -3420,33 +3542,13 @@ void do_format_arg(BasicWriter<Char> &writer, const format_arg &arg,
       spec.width_ = internal::parse_nonnegative_int(s);
     } else if (*s == '{') {
       ++s;
-      format_arg width_arg = ctx.parse_arg_id();
+      auto width_arg = ctx.parse_arg_id();
       if (*s++ != '}')
         FMT_THROW(format_error("invalid format string"));
-      ULongLong value = 0;
-      switch (width_arg.type) {
-      case format_arg::INT:
-        if (width_arg.int_value < 0)
-          FMT_THROW(format_error("negative width"));
-        value = width_arg.int_value;
-        break;
-      case format_arg::UINT:
-        value = width_arg.uint_value;
-        break;
-      case format_arg::LONG_LONG:
-        if (width_arg.long_long_value < 0)
-          FMT_THROW(format_error("negative width"));
-        value = width_arg.long_long_value;
-        break;
-      case format_arg::ULONG_LONG:
-        value = width_arg.ulong_long_value;
-        break;
-      default:
-        FMT_THROW(format_error("width is not integer"));
-      }
-      if (value > (std::numeric_limits<int>::max)())
+      ULongLong width = visit(internal::WidthHandler(), width_arg);
+      if (width > (std::numeric_limits<int>::max)())
         FMT_THROW(format_error("number is too big"));
-      spec.width_ = static_cast<int>(value);
+      spec.width_ = static_cast<int>(width);
     }
 
     // Parse precision.
@@ -3457,41 +3559,21 @@ void do_format_arg(BasicWriter<Char> &writer, const format_arg &arg,
         spec.precision_ = internal::parse_nonnegative_int(s);
       } else if (*s == '{') {
         ++s;
-        format_arg precision_arg = ctx.parse_arg_id();
+        auto precision_arg = ctx.parse_arg_id();
         if (*s++ != '}')
           FMT_THROW(format_error("invalid format string"));
-        ULongLong value = 0;
-        switch (precision_arg.type) {
-          case format_arg::INT:
-            if (precision_arg.int_value < 0)
-              FMT_THROW(format_error("negative precision"));
-            value = precision_arg.int_value;
-            break;
-          case format_arg::UINT:
-            value = precision_arg.uint_value;
-            break;
-          case format_arg::LONG_LONG:
-            if (precision_arg.long_long_value < 0)
-              FMT_THROW(format_error("negative precision"));
-            value = precision_arg.long_long_value;
-            break;
-          case format_arg::ULONG_LONG:
-            value = precision_arg.ulong_long_value;
-            break;
-          default:
-            FMT_THROW(format_error("precision is not integer"));
-        }
-        if (value > (std::numeric_limits<int>::max)())
+        ULongLong precision =
+          visit(internal::PrecisionHandler(), precision_arg);
+        if (precision > (std::numeric_limits<int>::max)())
           FMT_THROW(format_error("number is too big"));
-        spec.precision_ = static_cast<int>(value);
+        spec.precision_ = static_cast<int>(precision);
       } else {
         FMT_THROW(format_error("missing precision specifier"));
       }
-      if (arg.type <= format_arg::LAST_INTEGER_TYPE ||
-          arg.type == format_arg::POINTER) {
+      if (arg.is_integral() || arg.is_pointer()) {
         FMT_THROW(format_error(
             fmt::format("precision not allowed in {} format specifier",
-            arg.type == format_arg::POINTER ? "pointer" : "integer")));
+            arg.is_pointer() ? "pointer" : "integer")));
       }
     }
 
@@ -3510,7 +3592,7 @@ void do_format_arg(BasicWriter<Char> &writer, const format_arg &arg,
 /** Formats arguments and writes the output to the writer. */
 template <typename ArgFormatter, typename Char, typename Context>
 void vformat(BasicWriter<Char> &writer, BasicCStringRef<Char> format_str,
-             basic_format_args<Context> args) {
+             basic_format_args<Context, Char> args) {
   basic_format_context<Char> ctx(format_str.c_str(), args);
   const Char *&s = ctx.ptr();
   const Char *start = s;
@@ -3536,7 +3618,7 @@ void vformat(BasicWriter<Char> &writer, BasicCStringRef<Char> format_str,
 template <typename Char>
 inline void BasicWriter<Char>::vwrite(
     BasicCStringRef<Char> format,
-    basic_format_args<basic_format_context<Char>> args) {
+    basic_format_args<basic_format_context<Char>, Char> args) {
   vformat<ArgFormatter<Char>>(*this, format, args);
 }
 }  // namespace fmt
diff --git a/fmt/printf.h b/fmt/printf.h
index 386acf98..c6700185 100644
--- a/fmt/printf.h
+++ b/fmt/printf.h
@@ -40,7 +40,7 @@ struct IntChecker<true> {
   static bool fits_in_int(int) { return true; }
 };
 
-class PrecisionHandler {
+class PrintfPrecisionHandler {
  public:
   template <typename T>
   typename std::enable_if<std::is_integral<T>::value, int>::type
@@ -80,14 +80,14 @@ struct is_same<T, T> {
   enum { value = 1 };
 };
 
-template <typename T>
+template <typename T, typename Char>
 class ArgConverter {
  private:
-  format_arg &arg_;
-  wchar_t type_;
+  basic_format_arg<Char> &arg_;
+  Char type_;
 
  public:
-  ArgConverter(format_arg &arg, wchar_t type)
+  ArgConverter(basic_format_arg<Char> &arg, Char type)
     : arg_(arg), type_(type) {}
 
   void operator()(bool value) {
@@ -101,27 +101,27 @@ class ArgConverter {
     bool is_signed = type_ == 'd' || type_ == 'i';
     typedef typename internal::Conditional<
         is_same<T, void>::value, U, T>::type TargetType;
+    typedef basic_format_context<Char> format_context;
     if (sizeof(TargetType) <= sizeof(int)) {
       // Extra casts are used to silence warnings.
       if (is_signed) {
-        arg_.type = format_arg::INT;
-        arg_.int_value = static_cast<int>(static_cast<TargetType>(value));
+        arg_ = internal::MakeArg<format_context>(
+          static_cast<int>(static_cast<TargetType>(value)));
       } else {
-        arg_.type = format_arg::UINT;
         typedef typename internal::MakeUnsigned<TargetType>::Type Unsigned;
-        arg_.uint_value = static_cast<unsigned>(static_cast<Unsigned>(value));
+        arg_ = internal::MakeArg<format_context>(
+          static_cast<unsigned>(static_cast<Unsigned>(value)));
       }
     } else {
       if (is_signed) {
-        arg_.type = format_arg::LONG_LONG;
         // glibc's printf doesn't sign extend arguments of smaller types:
         //   std::printf("%lld", -42);  // prints "4294967254"
         // but we don't have to do the same because it's a UB.
-        arg_.long_long_value = static_cast<LongLong>(value);
+        arg_ = internal::MakeArg<format_context>(
+          static_cast<LongLong>(value));
       } else {
-        arg_.type = format_arg::ULONG_LONG;
-        arg_.ulong_long_value =
-            static_cast<typename internal::MakeUnsigned<U>::Type>(value);
+        arg_ = internal::MakeArg<format_context>(
+          static_cast<typename internal::MakeUnsigned<U>::Type>(value));
       }
     }
   }
@@ -137,26 +137,27 @@ class ArgConverter {
 // If T is void, the argument is converted to corresponding signed or unsigned
 // type depending on the type specifier: 'd' and 'i' - signed, other -
 // unsigned).
-template <typename T>
-void convert_arg(format_arg &arg, wchar_t type) {
-  visit(ArgConverter<T>(arg, type), arg);
+template <typename T, typename Char>
+void convert_arg(basic_format_arg<Char> &arg, Char type) {
+  visit(ArgConverter<T, Char>(arg, type), arg);
 }
 
 // Converts an integer argument to char for printf.
+template <typename Char>
 class CharConverter {
  private:
-  format_arg &arg_;
+  basic_format_arg<Char> &arg_;
 
   FMT_DISALLOW_COPY_AND_ASSIGN(CharConverter);
 
  public:
-  explicit CharConverter(format_arg &arg) : arg_(arg) {}
+  explicit CharConverter(basic_format_arg<Char> &arg) : arg_(arg) {}
 
   template <typename T>
   typename std::enable_if<std::is_integral<T>::value>::type
       operator()(T value) {
-    arg_.type = format_arg::CHAR;
-    arg_.int_value = static_cast<char>(value);
+    arg_ =
+      internal::MakeArg<basic_format_context<Char>>(static_cast<char>(value));
   }
 
   template <typename T>
@@ -168,14 +169,14 @@ class CharConverter {
 
 // Checks if an argument is a valid printf width specifier and sets
 // left alignment if it is negative.
-class WidthHandler {
+class PrintfWidthHandler {
  private:
   FormatSpec &spec_;
 
-  FMT_DISALLOW_COPY_AND_ASSIGN(WidthHandler);
+  FMT_DISALLOW_COPY_AND_ASSIGN(PrintfWidthHandler);
 
  public:
-  explicit WidthHandler(FormatSpec &spec) : spec_(spec) {}
+  explicit PrintfWidthHandler(FormatSpec &spec) : spec_(spec) {}
 
   template <typename T>
   typename std::enable_if<std::is_integral<T>::value, unsigned>::type
@@ -239,7 +240,7 @@ class PrintfArgFormatter : public internal::ArgFormatterBase<Char> {
   }
 
   /** Formats a character. */
-  void operator()(wchar_t value) {
+  void operator()(Char value) {
     const FormatSpec &fmt_spec = this->spec();
     BasicWriter<Char> &w = this->writer();
     if (fmt_spec.type_ && fmt_spec.type_ != 'c')
@@ -282,7 +283,7 @@ class PrintfArgFormatter : public internal::ArgFormatterBase<Char> {
   /** Formats an argument of a custom (user-defined) type. */
   void operator()(format_arg::CustomValue c) {
     const Char format_str[] = {'}', '\0'};
-    auto args = basic_format_args<basic_format_context<Char>>();
+    auto args = basic_format_args<basic_format_context<Char>, Char>();
     basic_format_context<Char> ctx(format_str, args);
     c.format(&this->writer(), c.value, &ctx);
   }
@@ -305,7 +306,7 @@ class printf_context :
 
   // Returns the argument with specified index or, if arg_index is equal
   // to the maximum unsigned value, the next argument.
-  format_arg get_arg(
+  basic_format_arg<Char> get_arg(
       const Char *s,
       unsigned arg_index = (std::numeric_limits<unsigned>::max)());
 
@@ -321,7 +322,7 @@ class printf_context :
    \endrst
    */
   explicit printf_context(BasicCStringRef<Char> format_str,
-                          basic_format_args<printf_context> args)
+                          basic_format_args<printf_context, Char> args)
     : Base(format_str.c_str(), args) {}
 
   /** Formats stored arguments and writes the output to the writer. */
@@ -355,11 +356,12 @@ void printf_context<Char, AF>::parse_flags(FormatSpec &spec, const Char *&s) {
 }
 
 template <typename Char, typename AF>
-format_arg printf_context<Char, AF>::get_arg(const Char *s,
-                                             unsigned arg_index) {
+basic_format_arg<Char> printf_context<Char, AF>::get_arg(
+    const Char *s, unsigned arg_index) {
   (void)s;
   const char *error = 0;
-  format_arg arg = arg_index == std::numeric_limits<unsigned>::max() ?
+  basic_format_arg<Char> arg =
+    arg_index == std::numeric_limits<unsigned>::max() ?
     this->next_arg(error) : Base::get_arg(arg_index - 1, error);
   if (error)
     FMT_THROW(format_error(!*s ? "invalid format string" : error));
@@ -395,7 +397,7 @@ unsigned printf_context<Char, AF>::parse_header(
     spec.width_ = internal::parse_nonnegative_int(s);
   } else if (*s == '*') {
     ++s;
-    spec.width_ = visit(internal::WidthHandler(spec), get_arg(s));
+    spec.width_ = visit(internal::PrintfWidthHandler(spec), get_arg(s));
   }
   return arg_index;
 }
@@ -427,15 +429,15 @@ void printf_context<Char, AF>::format(BasicWriter<Char> &writer) {
         spec.precision_ = static_cast<int>(internal::parse_nonnegative_int(s));
       } else if (*s == '*') {
         ++s;
-        spec.precision_ = visit(internal::PrecisionHandler(), get_arg(s));
+        spec.precision_ = visit(internal::PrintfPrecisionHandler(), get_arg(s));
       }
     }
 
-    format_arg arg = get_arg(s, arg_index);
+    basic_format_arg<Char> arg = get_arg(s, arg_index);
     if (spec.flag(HASH_FLAG) && visit(internal::IsZeroInt(), arg))
       spec.flags_ &= ~internal::to_unsigned<int>(HASH_FLAG);
     if (spec.fill_ == '0') {
-      if (arg.type <= format_arg::LAST_NUMERIC_TYPE)
+      if (arg.is_numeric())
         spec.align_ = ALIGN_NUMERIC;
       else
         spec.fill_ = ' ';  // Ignore '0' flag for non-numeric types.
@@ -478,7 +480,7 @@ void printf_context<Char, AF>::format(BasicWriter<Char> &writer) {
     if (!*s)
       FMT_THROW(format_error("invalid format string"));
     spec.type_ = static_cast<char>(*s++);
-    if (arg.type <= format_arg::LAST_INTEGER_TYPE) {
+    if (arg.is_integral()) {
       // Normalize type.
       switch (spec.type_) {
       case 'i': case 'u':
@@ -486,7 +488,7 @@ void printf_context<Char, AF>::format(BasicWriter<Char> &writer) {
         break;
       case 'c':
         // TODO: handle wchar_t
-        visit(internal::CharConverter(arg), arg);
+        visit(internal::CharConverter<Char>(arg), arg);
         break;
       }
     }
@@ -509,12 +511,13 @@ void format_value(BasicWriter<Char> &w, const T &value,
 
 template <typename Char>
 void printf(BasicWriter<Char> &w, BasicCStringRef<Char> format,
-            basic_format_args<printf_context<Char>> args) {
+            basic_format_args<printf_context<Char>, Char> args) {
   printf_context<Char>(format, args).format(w);
 }
 
-inline std::string vsprintf(CStringRef format,
-                            basic_format_args<printf_context<char>> args) {
+typedef basic_format_args<printf_context<char>, char> printf_args;
+
+inline std::string vsprintf(CStringRef format, printf_args args) {
   MemoryWriter w;
   printf(w, format, args);
   return w.str();
@@ -534,8 +537,9 @@ inline std::string sprintf(CStringRef format_str, const Args & ... args) {
   return vsprintf(format_str, make_xformat_args<printf_context<char>>(args...));
 }
 
-inline std::wstring vsprintf(WCStringRef format,
-                             basic_format_args<printf_context<wchar_t>> args) {
+inline std::wstring vsprintf(
+    WCStringRef format,
+    basic_format_args<printf_context<wchar_t>, wchar_t> args) {
   WMemoryWriter w;
   printf(w, format, args);
   return w.str();
@@ -547,8 +551,7 @@ inline std::wstring sprintf(WCStringRef format_str, const Args & ... args) {
   return vsprintf(format_str, vargs);
 }
 
-FMT_API int vfprintf(std::FILE *f, CStringRef format,
-                     basic_format_args<printf_context<char>> args);
+FMT_API int vfprintf(std::FILE *f, CStringRef format, printf_args args);
 
 /**
   \rst
@@ -565,8 +568,7 @@ inline int fprintf(std::FILE *f, CStringRef format_str, const Args & ... args) {
   return vfprintf(f, format_str, vargs);
 }
 
-inline int vprintf(CStringRef format,
-                   basic_format_args<printf_context<char>> args) {
+inline int vprintf(CStringRef format, printf_args args) {
   return vfprintf(stdout, format, args);
 }
 
@@ -584,8 +586,7 @@ inline int printf(CStringRef format_str, const Args & ... args) {
   return vprintf(format_str, make_xformat_args<printf_context<char>>(args...));
 }
 
-inline int vfprintf(std::ostream &os, CStringRef format_str,
-                    basic_format_args<printf_context<char>> args) {
+inline int vfprintf(std::ostream &os, CStringRef format_str, printf_args args) {
   MemoryWriter w;
   printf(w, format_str, args);
   internal::write(os, w);
diff --git a/test/custom-formatter-test.cc b/test/custom-formatter-test.cc
index 7601aeb5..51bed768 100644
--- a/test/custom-formatter-test.cc
+++ b/test/custom-formatter-test.cc
@@ -63,7 +63,7 @@ typedef fmt::printf_context<char, CustomPrintfArgFormatter>
 
 std::string custom_vsprintf(
     const char* format_str,
-    fmt::basic_format_args<CustomPrintfFormatter> args) {
+    fmt::basic_format_args<CustomPrintfFormatter, char> args) {
   fmt::MemoryWriter writer;
   CustomPrintfFormatter formatter(format_str, args);
   formatter.format(writer);
diff --git a/test/format-impl-test.cc b/test/format-impl-test.cc
index c63b6b97..ff702a53 100644
--- a/test/format-impl-test.cc
+++ b/test/format-impl-test.cc
@@ -41,13 +41,25 @@
 #undef min
 #undef max
 
+template <typename T>
+struct ValueExtractor {
+  T operator()(T value) {
+    return value;
+  }
+
+  template <typename U>
+  T operator()(U) {
+    throw std::runtime_error(fmt::format("invalid type {}", typeid(U).name()));
+    return T();
+  }
+};
+
 TEST(FormatTest, ArgConverter) {
   using fmt::format_arg;
-  format_arg arg = format_arg();
-  arg.type = format_arg::LONG_LONG;
-  arg.long_long_value = std::numeric_limits<fmt::LongLong>::max();
-  visit(fmt::internal::ArgConverter<fmt::LongLong>(arg, 'd'), arg);
-  EXPECT_EQ(format_arg::LONG_LONG, arg.type);
+  fmt::LongLong value = std::numeric_limits<fmt::LongLong>::max();
+  format_arg arg = fmt::internal::MakeArg<fmt::format_context>(value);
+  visit(fmt::internal::ArgConverter<fmt::LongLong, char>(arg, 'd'), arg);
+  EXPECT_EQ(value, visit(ValueExtractor<fmt::LongLong>(), arg));
 }
 
 TEST(FormatTest, FormatNegativeNaN) {
diff --git a/test/util-test.cc b/test/util-test.cc
index 3371ef20..c39b0abf 100644
--- a/test/util-test.cc
+++ b/test/util-test.cc
@@ -49,13 +49,17 @@
 
 #include "fmt/format.h"
 
+#undef min
 #undef max
 
+using fmt::basic_format_arg;
 using fmt::format_arg;
 using fmt::Buffer;
 using fmt::StringRef;
 using fmt::internal::MemoryBuffer;
+using fmt::internal::Value;
 
+using testing::_;
 using testing::Return;
 using testing::StrictMock;
 
@@ -70,11 +74,9 @@ void format_value(fmt::BasicWriter<Char> &w, Test,
 }
 
 template <typename Char, typename T>
-format_arg make_arg(const T &value) {
-  typedef fmt::internal::MakeValue< fmt::basic_format_context<Char> > MakeValue;
-  format_arg arg = MakeValue(value);
-  arg.type = fmt::internal::type<T>();
-  return arg;
+basic_format_arg<Char> make_arg(const T &value) {
+  typedef fmt::internal::MakeArg< fmt::basic_format_context<Char> > MakeArg;
+  return MakeArg(value);
 }
 }  // namespace
 
@@ -406,175 +408,9 @@ TEST(UtilTest, Increment) {
   EXPECT_STREQ("200", s);
 }
 
-template <format_arg::Type>
-struct ArgInfo;
-
-#define ARG_INFO(type_code, Type, field) \
-  template <> \
-  struct ArgInfo<format_arg::type_code> { \
-    static Type get(const format_arg &arg) { return arg.field; } \
-  }
-
-ARG_INFO(INT, int, int_value);
-ARG_INFO(UINT, unsigned, uint_value);
-ARG_INFO(LONG_LONG, fmt::LongLong, long_long_value);
-ARG_INFO(ULONG_LONG, fmt::ULongLong, ulong_long_value);
-ARG_INFO(BOOL, int, int_value);
-ARG_INFO(CHAR, int, int_value);
-ARG_INFO(DOUBLE, double, double_value);
-ARG_INFO(LONG_DOUBLE, long double, long_double_value);
-ARG_INFO(CSTRING, const char *, string.value);
-ARG_INFO(STRING, const char *, string.value);
-ARG_INFO(WSTRING, const wchar_t *, wstring.value);
-ARG_INFO(POINTER, const void *, pointer);
-ARG_INFO(CUSTOM, format_arg::CustomValue, custom);
-
-#define CHECK_ARG_INFO(Type, field, value) { \
-  format_arg arg = format_arg(); \
-  arg.field = value; \
-  EXPECT_EQ(value, ArgInfo<format_arg::Type>::get(arg)); \
-}
-
-TEST(ArgTest, ArgInfo) {
-  CHECK_ARG_INFO(INT, int_value, 42);
-  CHECK_ARG_INFO(UINT, uint_value, 42u);
-  CHECK_ARG_INFO(LONG_LONG, long_long_value, 42);
-  CHECK_ARG_INFO(ULONG_LONG, ulong_long_value, 42u);
-  CHECK_ARG_INFO(DOUBLE, double_value, 4.2);
-  CHECK_ARG_INFO(LONG_DOUBLE, long_double_value, 4.2);
-  CHECK_ARG_INFO(CHAR, int_value, 'x');
-  const char STR[] = "abc";
-  CHECK_ARG_INFO(CSTRING, string.value, STR);
-  const wchar_t WSTR[] = L"abc";
-  CHECK_ARG_INFO(WSTRING, wstring.value, WSTR);
-  int p = 0;
-  CHECK_ARG_INFO(POINTER, pointer, &p);
-  format_arg arg = format_arg();
-  arg.custom.value = &p;
-  EXPECT_EQ(&p, ArgInfo<format_arg::CUSTOM>::get(arg).value);
-}
-
-#define EXPECT_ARG_(Char, type_code, MakeArgType, ExpectedType, value) { \
-  MakeArgType input = static_cast<MakeArgType>(value); \
-  format_arg arg = make_arg<Char>(input); \
-  EXPECT_EQ(format_arg::type_code, arg.type); \
-  ExpectedType expected_value = static_cast<ExpectedType>(value); \
-  EXPECT_EQ(expected_value, ArgInfo<format_arg::type_code>::get(arg)); \
-}
-
-#define EXPECT_ARG(type_code, Type, value) \
-  EXPECT_ARG_(char, type_code, Type, Type, value)
-
-#define EXPECT_ARGW(type_code, Type, value) \
-  EXPECT_ARG_(wchar_t, type_code, Type, Type, value)
-
-TEST(ArgTest, MakeArg) {
-  // Test bool.
-  EXPECT_ARG_(char, BOOL, bool, int, true);
-  EXPECT_ARG_(wchar_t, BOOL, bool, int, true);
-
-  // Test char.
-  EXPECT_ARG(CHAR, char, 'a');
-  EXPECT_ARG(CHAR, char, CHAR_MIN);
-  EXPECT_ARG(CHAR, char, CHAR_MAX);
-
-  // Test wchar_t.
-  EXPECT_ARGW(CHAR, wchar_t, L'a');
-  EXPECT_ARGW(CHAR, wchar_t, WCHAR_MIN);
-  EXPECT_ARGW(CHAR, wchar_t, WCHAR_MAX);
-
-  // Test signed/unsigned char.
-  EXPECT_ARG(INT, signed char, 42);
-  EXPECT_ARG(INT, signed char, SCHAR_MIN);
-  EXPECT_ARG(INT, signed char, SCHAR_MAX);
-  EXPECT_ARG(UINT, unsigned char, 42);
-  EXPECT_ARG(UINT, unsigned char, UCHAR_MAX );
-
-  // Test short.
-  EXPECT_ARG(INT, short, 42);
-  EXPECT_ARG(INT, short, SHRT_MIN);
-  EXPECT_ARG(INT, short, SHRT_MAX);
-  EXPECT_ARG(UINT, unsigned short, 42);
-  EXPECT_ARG(UINT, unsigned short, USHRT_MAX);
-
-  // Test int.
-  EXPECT_ARG(INT, int, 42);
-  EXPECT_ARG(INT, int, INT_MIN);
-  EXPECT_ARG(INT, int, INT_MAX);
-  EXPECT_ARG(UINT, unsigned, 42);
-  EXPECT_ARG(UINT, unsigned, UINT_MAX);
-
-  // Test long.
-#if LONG_MAX == INT_MAX
-# define LONG INT
-# define ULONG UINT
-# define long_value int_value
-# define ulong_value uint_value
-#else
-# define LONG LONG_LONG
-# define ULONG ULONG_LONG
-# define long_value long_long_value
-# define ulong_value ulong_long_value
-#endif
-  EXPECT_ARG(LONG, long, 42);
-  EXPECT_ARG(LONG, long, LONG_MIN);
-  EXPECT_ARG(LONG, long, LONG_MAX);
-  EXPECT_ARG(ULONG, unsigned long, 42);
-  EXPECT_ARG(ULONG, unsigned long, ULONG_MAX);
-
-  // Test long long.
-  EXPECT_ARG(LONG_LONG, fmt::LongLong, 42);
-  EXPECT_ARG(LONG_LONG, fmt::LongLong, LLONG_MIN);
-  EXPECT_ARG(LONG_LONG, fmt::LongLong, LLONG_MAX);
-  EXPECT_ARG(ULONG_LONG, fmt::ULongLong, 42);
-  EXPECT_ARG(ULONG_LONG, fmt::ULongLong, ULLONG_MAX);
-
-  // Test float.
-  EXPECT_ARG(DOUBLE, float, 4.2);
-  EXPECT_ARG(DOUBLE, float, FLT_MIN);
-  EXPECT_ARG(DOUBLE, float, FLT_MAX);
-
-  // Test double.
-  EXPECT_ARG(DOUBLE, double, 4.2);
-  EXPECT_ARG(DOUBLE, double, DBL_MIN);
-  EXPECT_ARG(DOUBLE, double, DBL_MAX);
-
-  // Test long double.
-  EXPECT_ARG(LONG_DOUBLE, long double, 4.2);
-  EXPECT_ARG(LONG_DOUBLE, long double, LDBL_MIN);
-  EXPECT_ARG(LONG_DOUBLE, long double, LDBL_MAX);
-
-  // Test string.
-  char STR[] = "test";
-  EXPECT_ARG(CSTRING, char*, STR);
-  EXPECT_ARG(CSTRING, const char*, STR);
-  EXPECT_ARG(STRING, std::string, STR);
-  EXPECT_ARG(STRING, fmt::StringRef, STR);
-
-  // Test wide string.
-  wchar_t WSTR[] = L"test";
-  EXPECT_ARGW(WSTRING, wchar_t*, WSTR);
-  EXPECT_ARGW(WSTRING, const wchar_t*, WSTR);
-  EXPECT_ARGW(WSTRING, std::wstring, WSTR);
-  EXPECT_ARGW(WSTRING, fmt::WStringRef, WSTR);
-
-  int n = 42;
-  EXPECT_ARG(POINTER, void*, &n);
-  EXPECT_ARG(POINTER, const void*, &n);
-
-  ::Test t;
-  format_arg arg = make_arg<char>(t);
-  EXPECT_EQ(format_arg::CUSTOM, arg.type);
-  EXPECT_EQ(&t, arg.custom.value);
-  fmt::MemoryWriter w;
-  fmt::format_context ctx("}", fmt::format_args());
-  arg.custom.format(&w, &t, &ctx);
-  EXPECT_EQ("test", w.str());
-}
-
 TEST(UtilTest, FormatArgs) {
   fmt::format_args args;
-  EXPECT_EQ(format_arg::NONE, args[1].type);
+  EXPECT_FALSE(args[1]);
 }
 
 struct CustomFormatter {
@@ -595,73 +431,163 @@ TEST(UtilTest, MakeValueWithCustomFormatter) {
   EXPECT_TRUE(ctx.called);
 }
 
-struct Result {
-  format_arg arg;
+namespace fmt {
+namespace internal {
 
-  Result() : arg(make_arg<char>(0xdeadbeef)) {}
-
-  template <typename T>
-  Result(const T& value) : arg(make_arg<char>(value)) {}
-  Result(const wchar_t *s) : arg(make_arg<wchar_t>(s)) {}
-};
-
-struct TestVisitor {
-  Result operator()(int value) { return value; }
-  Result operator()(unsigned value) { return value; }
-  Result operator()(fmt::LongLong value) { return value; }
-  Result operator()(fmt::ULongLong value) { return value; }
-  Result operator()(double value) { return value; }
-  Result operator()(long double value) { return value; }
-  Result operator()(wchar_t value) { return static_cast<char>(value); }
-  Result operator()(const char *s) { return s; }
-  Result operator()(fmt::format_arg::StringValue<char> s) {
-    return s.value;
-  }
-  Result operator()(fmt::format_arg::StringValue<wchar_t> s) {
-    return s.value;
-  }
-  Result operator()(const void *p) { return p; }
-  Result operator()(fmt::format_arg::CustomValue c) {
-    return *static_cast<const ::Test*>(c.value);
-  }
-};
-
-#define EXPECT_RESULT_(Char, type_code, value) { \
-  format_arg arg = make_arg<Char>(value); \
-  Result result = fmt::visit(TestVisitor(), arg); \
-  EXPECT_EQ(format_arg::type_code, result.arg.type); \
-  EXPECT_EQ(value, ArgInfo<format_arg::type_code>::get(result.arg)); \
+bool operator==(Value::CustomValue lhs, Value::CustomValue rhs) {
+  return lhs.value == rhs.value;
 }
 
-#define EXPECT_RESULT(type_code, value) \
-  EXPECT_RESULT_(char, type_code, value)
-#define EXPECT_RESULTW(type_code, value) \
-  EXPECT_RESULT_(wchar_t, type_code, value)
+template <typename T>
+bool operator==(Value::StringValue<T> lhs, Value::StringValue<T> rhs) {
+  return std::basic_string<T>(lhs.value, lhs.size) ==
+         std::basic_string<T>(rhs.value, rhs.size);
+}
+}
+}
 
-TEST(ArgVisitorTest, VisitAll) {
-  EXPECT_RESULT(INT, 42);
-  EXPECT_RESULT(UINT, 42u);
-  EXPECT_RESULT(LONG_LONG, 42ll);
-  EXPECT_RESULT(ULONG_LONG, 42ull);
-  EXPECT_RESULT(DOUBLE, 4.2);
-  EXPECT_RESULT(LONG_DOUBLE, 4.2l);
-  EXPECT_RESULT(CHAR, 'x');
-  const char STR[] = "abc";
-  EXPECT_RESULT(CSTRING, STR);
-  const wchar_t WSTR[] = L"abc";
-  EXPECT_RESULTW(WSTRING, WSTR);
-  const void *p = STR;
-  EXPECT_RESULT(POINTER, p);
-  ::Test t;
-  Result result = visit(TestVisitor(), make_arg<char>(t));
-  EXPECT_EQ(format_arg::CUSTOM, result.arg.type);
-  EXPECT_EQ(&t, result.arg.custom.value);
+template <typename T>
+struct MockVisitor {
+  // Use a unique result type to make sure that there are no undesirable
+  // conversions.
+  struct Result {};
+
+  MockVisitor() {
+    ON_CALL(*this, visit(_)).WillByDefault(Return(Result()));
+  }
+
+  MOCK_METHOD1_T(visit, Result (T value));
+  MOCK_METHOD0_T(unexpected, void ());
+
+  Result operator()(T value) { return visit(value); }
+
+  template <typename U>
+  Result operator()(U value) {
+    unexpected();
+    return Result();
+  }
+};
+
+template <typename T>
+struct VisitType { typedef T Type; };
+
+#define VISIT_TYPE(Type_, VisitType_) \
+  template <> \
+  struct VisitType<Type_> { typedef VisitType_ Type; }
+
+VISIT_TYPE(signed char, int);
+VISIT_TYPE(unsigned char, unsigned);
+VISIT_TYPE(short, int);
+VISIT_TYPE(unsigned short, unsigned);
+
+#if LONG_MAX == INT_MAX
+VISIT_TYPE(long, int);
+VISIT_TYPE(unsigned long, unsigned);
+#else
+VISIT_TYPE(long, fmt::LongLong);
+VISIT_TYPE(unsigned long, fmt::ULongLong);
+#endif
+
+VISIT_TYPE(float, double);
+
+#define CHECK_ARG_(Char, expected, value) { \
+  testing::StrictMock<MockVisitor<decltype(expected)>> visitor; \
+  EXPECT_CALL(visitor, visit(expected)); \
+  fmt::visit(visitor, make_arg<Char>(value)); \
+}
+
+#define CHECK_ARG(value) { \
+  typename VisitType<decltype(value)>::Type expected = value; \
+  CHECK_ARG_(char, expected, value) \
+  CHECK_ARG_(wchar_t, expected, value) \
+}
+
+template <typename T>
+class NumericArgTest : public testing::Test {};
+
+typedef ::testing::Types<
+  bool, signed char, unsigned char, signed, unsigned short,
+  int, unsigned, long, unsigned long, fmt::LongLong, fmt::ULongLong,
+  float, double, long double> Types;
+TYPED_TEST_CASE(NumericArgTest, Types);
+
+template <typename T>
+typename std::enable_if<std::is_integral<T>::value, T>::type test_value() {
+  return static_cast<T>(42);
+}
+
+template <typename T>
+typename std::enable_if<std::is_floating_point<T>::value, T>::type
+    test_value() {
+  return static_cast<T>(4.2);
+}
+
+TYPED_TEST(NumericArgTest, MakeAndVisit) {
+  CHECK_ARG(test_value<TypeParam>());
+  CHECK_ARG(std::numeric_limits<TypeParam>::min());
+  CHECK_ARG(std::numeric_limits<TypeParam>::max());
+}
+
+TEST(UtilTest, CharArg) {
+  CHECK_ARG_(char, 'a', 'a');
+  CHECK_ARG_(wchar_t, L'a', 'a');
+  CHECK_ARG_(wchar_t, L'a', L'a');
+}
+
+TEST(UtilTest, StringArg) {
+  char str_data[] = "test";
+  char *str = str_data;
+  const char *cstr = str;
+  CHECK_ARG_(char, cstr, str);
+  CHECK_ARG_(wchar_t, cstr, str);
+  CHECK_ARG(cstr);
+
+  Value::StringValue<char> strval = {str, 4};
+  CHECK_ARG_(char, strval, std::string(str));
+  CHECK_ARG_(wchar_t, strval, std::string(str));
+  CHECK_ARG_(char, strval, fmt::StringRef(str));
+  CHECK_ARG_(wchar_t, strval, fmt::StringRef(str));
+}
+
+TEST(UtilTest, WStringArg) {
+  wchar_t str_data[] = L"test";
+  wchar_t *str = str_data;
+  const wchar_t *cstr = str;
+
+  Value::StringValue<wchar_t> strval = {str, 4};
+  CHECK_ARG_(wchar_t, strval, str);
+  CHECK_ARG_(wchar_t, strval, cstr);
+  CHECK_ARG_(wchar_t, strval, std::wstring(str));
+  CHECK_ARG_(wchar_t, strval, fmt::WStringRef(str));
+}
+
+TEST(UtilTest, PointerArg) {
+  void *p = 0;
+  const void *cp = 0;
+  CHECK_ARG_(char, cp, p);
+  CHECK_ARG_(wchar_t, cp, p);
+  CHECK_ARG(cp);
+}
+
+TEST(UtilTest, CustomArg) {
+  ::Test test;
+  typedef MockVisitor<Value::CustomValue> Visitor;
+  testing::StrictMock<Visitor> visitor;
+  EXPECT_CALL(visitor, visit(_)).WillOnce(
+        testing::Invoke([&](Value::CustomValue custom) {
+    EXPECT_EQ(&test, custom.value);
+    fmt::MemoryWriter w;
+    fmt::format_context ctx("}", fmt::format_args());
+    custom.format(&w, &test, &ctx);
+    EXPECT_EQ("test", w.str());
+    return Visitor::Result();
+  }));
+  fmt::visit(visitor, make_arg<char>(test));
 }
 
 TEST(ArgVisitorTest, VisitInvalidArg) {
   format_arg arg = format_arg();
-  arg.type = static_cast<format_arg::Type>(format_arg::NONE);
-  EXPECT_ASSERT(visit(TestVisitor(), arg), "invalid argument type");
+  EXPECT_ASSERT(visit(MockVisitor<int>(), arg), "invalid argument type");
 }
 
 // Tests fmt::internal::count_digits for integer type Int.