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Support named args in dynamic_format_arg_store (#1655). (#1663)

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Dynamic arguments storage. Implementation of enhancement from issue
#1170.
This commit is contained in:
Vladimir Solontsov 2020-05-09 16:25:03 +03:00 committed by GitHub
parent 7f723fbcb8
commit 68201831a5
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2 changed files with 178 additions and 49 deletions
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167
include/fmt/core.h
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@ -610,6 +610,7 @@ using wformat_parse_context = basic_format_parse_context<wchar_t>;
template <typename Context> class basic_format_arg;
template <typename Context> class basic_format_args;
template <typename Context> class dynamic_format_arg_store;
// A formatter for objects of type T.
template <typename T, typename Char = char, typename Enable = void>
@ -1111,6 +1112,7 @@ template <typename Context> class basic_format_arg {
friend class basic_format_args<Context>;
friend class internal::arg_map<Context>;
friend class dynamic_format_arg_store<Context>;
using char_type = typename Context::char_type;
@ -1252,10 +1254,14 @@ inline basic_format_arg<Context> make_arg(const T& value) {
}
template <typename T> struct is_reference_wrapper : std::false_type {};
template <typename T>
struct is_reference_wrapper<std::reference_wrapper<T>> : std::true_type {};
template <typename T> const T& unwrap(const T& v) { return v; }
template <typename T> const T& unwrap(const std::reference_wrapper<T>& v) {
return static_cast<const T&>(v);
}
class dynamic_arg_list {
// Workaround for clang's -Wweak-vtables. Unlike for regular classes, for
// templates it doesn't complain about inability to deduce single translation
@ -1404,6 +1410,50 @@ inline format_arg_store<Context, Args...> make_format_args(
return {args...};
}
namespace internal {
template <typename Char> struct named_arg_base {
const Char* name;
// Serialized value<context>.
mutable char data[sizeof(basic_format_arg<buffer_context<Char>>)];
named_arg_base(const Char* nm) : name(nm) {}
template <typename Context> basic_format_arg<Context> deserialize() const {
basic_format_arg<Context> arg;
std::memcpy(&arg, data, sizeof(basic_format_arg<Context>));
return arg;
}
};
struct view {};
template <typename T, typename Char>
struct named_arg : view, named_arg_base<Char> {
const T& value;
named_arg(const Char* name, const T& val)
: named_arg_base<Char>(name), value(val) {}
};
} // namespace internal
/**
\rst
Returns a named argument to be used in a formatting function. It should only
be used in a call to a formatting function.
**Example**::
fmt::print("Elapsed time: {s:.2f} seconds", fmt::arg("s", 1.23));
\endrst
*/
template <typename Char, typename T>
inline internal::named_arg<T, Char> arg(const Char* name, const T& arg) {
static_assert(!internal::is_named_arg<T>(), "nested named arguments");
return {name, arg};
}
/**
\rst
A dynamic version of `fmt::format_arg_store<>`.
@ -1434,8 +1484,7 @@ class dynamic_format_arg_store
std::is_same<T, internal::std_string_view<char_type>>::value ||
(mapped_type != internal::type::cstring_type &&
mapped_type != internal::type::string_type &&
mapped_type != internal::type::custom_type &&
mapped_type != internal::type::named_arg_type))
mapped_type != internal::type::custom_type))
};
};
@ -1445,6 +1494,7 @@ class dynamic_format_arg_store
// Storage of basic_format_arg must be contiguous.
std::vector<basic_format_arg<Context>> data_;
std::vector<internal::named_arg_info<char_type>> named_info_;
// Storage of arguments not fitting into basic_format_arg must grow
// without relocation because items in data_ refer to it.
@ -1453,13 +1503,38 @@ class dynamic_format_arg_store
friend class basic_format_args<Context>;
unsigned long long get_types() const {
return internal::is_unpacked_bit | data_.size();
return internal::is_unpacked_bit | data_.size() |
(named_info_.empty() ? 0ULL
: static_cast<unsigned long long>(
internal::has_named_args_bit));
}
const basic_format_arg<Context>* data() const {
return named_info_.empty() ? data_.data() : data_.data() + 1;
}
template <typename T> void emplace_arg(const T& arg) {
data_.emplace_back(internal::make_arg<Context>(arg));
}
template <typename T>
void emplace_arg(const internal::named_arg<T, char_type>& arg) {
if (named_info_.empty()) {
constexpr const internal::named_arg_info<char_type>* zero_ptr{nullptr};
data_.insert(data_.begin(), {zero_ptr, 0});
}
data_.emplace_back(
internal::make_arg<Context>(internal::unwrap(arg.value)));
auto pop_one = [](std::vector<basic_format_arg<Context>>* data) {
data->pop_back();
};
std::unique_ptr<std::vector<basic_format_arg<Context>>, decltype(pop_one)>
guard{&data_, pop_one};
named_info_.push_back({arg.name, static_cast<int>(data_.size() - 2u)});
data_[0].value_.named_args = {named_info_.data(), named_info_.size()};
guard.release();
}
public:
/**
\rst
@ -1485,19 +1560,54 @@ class dynamic_format_arg_store
if (internal::const_check(need_copy<T>::value))
emplace_arg(dynamic_args_.push<stored_type<T>>(arg));
else
emplace_arg(arg);
emplace_arg(internal::unwrap(arg));
}
/**
\rst
Adds a reference to the argument into the dynamic store for later passing to
a formating function.
a formating function. Supports named arguments wrapped in
std::reference_wrapper (via std::ref()/std::cref()).
**Example**::
fmt::dynamic_format_arg_store<fmt::format_context> store;
char str[] = "1234567890";
store.push_back(std::cref(str));
int a1_val{42};
auto a1 = fmt::arg("a1_", a1_val);
store.push_back(std::cref(a1));
// Changing str affects the output but only for string and custom types.
str[0] = 'X';
std::string result = fmt::vformat("{} and {a1_}");
assert(result == "X234567890 and 42");
\endrst
*/
template <typename T> void push_back(std::reference_wrapper<T> arg) {
static_assert(
need_copy<T>::value,
internal::is_named_arg<typename std::remove_cv<T>::type>::value ||
need_copy<T>::value,
"objects of built-in types and string views are always copied");
emplace_arg(arg.get());
}
/**
Adds named argument into the dynamic store for later passing to a formating
function. std::reference_wrapper is supported to avoid copying of the
argument.
*/
template <typename T>
void push_back(const internal::named_arg<T, char_type>& arg) {
const char_type* arg_name =
dynamic_args_.push<std::basic_string<char_type>>(arg.name).c_str();
if (internal::const_check(need_copy<T>::value)) {
emplace_arg(
fmt::arg(arg_name, dynamic_args_.push<stored_type<T>>(arg.value)));
} else {
emplace_arg(fmt::arg(arg_name, arg.value));
}
}
};
/**
@ -1582,7 +1692,7 @@ template <typename Context> class basic_format_args {
\endrst
*/
FMT_INLINE basic_format_args(const dynamic_format_arg_store<Context>& store)
: basic_format_args(store.get_types(), store.data_.data()) {}
: basic_format_args(store.get_types(), store.data()) {}
/**
\rst
@ -1644,31 +1754,6 @@ template <typename Container>
struct is_contiguous_back_insert_iterator<std::back_insert_iterator<Container>>
: is_contiguous<Container> {};
template <typename Char> struct named_arg_base {
const Char* name;
// Serialized value<context>.
mutable char data[sizeof(basic_format_arg<buffer_context<Char>>)];
named_arg_base(const Char* nm) : name(nm) {}
template <typename Context> basic_format_arg<Context> deserialize() const {
basic_format_arg<Context> arg;
std::memcpy(&arg, data, sizeof(basic_format_arg<Context>));
return arg;
}
};
struct view {};
template <typename T, typename Char>
struct named_arg : view, named_arg_base<Char> {
const T& value;
named_arg(const Char* name, const T& val)
: named_arg_base<Char>(name), value(val) {}
};
// Reports a compile-time error if S is not a valid format string.
template <typename..., typename S, FMT_ENABLE_IF(!is_compile_string<S>::value)>
FMT_INLINE void check_format_string(const S&) {
@ -1712,22 +1797,6 @@ inline void vprint_mojibake(std::FILE*, string_view, format_args) {}
#endif
} // namespace internal
/**
\rst
Returns a named argument to be used in a formatting function. It should only
be used in a call to a formatting function.
**Example**::
fmt::print("Elapsed time: {s:.2f} seconds", fmt::arg("s", 1.23));
\endrst
*/
template <typename Char, typename T>
inline internal::named_arg<T, Char> arg(const Char* name, const T& arg) {
static_assert(!internal::is_named_arg<T>(), "nested named arguments");
return {name, arg};
}
/** Formats a string and writes the output to ``out``. */
// GCC 8 and earlier cannot handle std::back_insert_iterator<Container> with
// vformat_to<ArgFormatter>(...) overload, so SFINAE on iterator type instead.

60
test/core-test.cc
View File

@ -456,6 +456,66 @@ TEST(FormatDynArgsTest, CustomFormat) {
EXPECT_EQ("cust=0 and cust=1 and cust=3", result);
}
TEST(FormatDynArgsTest, NamedInt) {
fmt::dynamic_format_arg_store<fmt::format_context> store;
store.push_back(fmt::arg("a1", 42));
std::string result = fmt::vformat("{a1}", store);
EXPECT_EQ("42", result);
}
TEST(FormatDynArgsTest, NamedStrings) {
fmt::dynamic_format_arg_store<fmt::format_context> store;
char str[]{"1234567890"};
store.push_back(fmt::arg("a1", str));
store.push_back(fmt::arg("a2", std::cref(str)));
str[0] = 'X';
std::string result = fmt::vformat(
"{a1} and {a2}",
store);
EXPECT_EQ("1234567890 and X234567890", result);
}
TEST(FormatDynArgsTest, NamedArgByRef) {
fmt::dynamic_format_arg_store<fmt::format_context> store;
// Note: fmt::arg() constructs an object which holds a reference
// to its value. It's not an aggregate, so it doesn't extend the
// reference lifetime. As a result, it's a very bad idea passing temporary
// as a named argument value. Only GCC with optimization level >0
// complains about this.
//
// A real life usecase is when you have both name and value alive
// guarantee their lifetime and thus don't want them to be copied into
// storages.
int a1_val{42};
auto a1 = fmt::arg("a1_", a1_val);
store.push_back("abc");
store.push_back(1.5f);
store.push_back(std::cref(a1));
std::string result = fmt::vformat(
"{a1_} and {} and {} and {}",
store);
EXPECT_EQ("42 and abc and 1.5 and 42", result);
}
TEST(FormatDynArgsTest, NamedCustomFormat) {
fmt::dynamic_format_arg_store<fmt::format_context> store;
custom_type c{};
store.push_back(fmt::arg("c1", c));
++c.i;
store.push_back(fmt::arg("c2", c));
++c.i;
store.push_back(fmt::arg("c_ref", std::cref(c)));
++c.i;
std::string result = fmt::vformat("{c1} and {c2} and {c_ref}", store);
EXPECT_EQ("cust=0 and cust=1 and cust=3", result);
}
struct copy_throwable {
copy_throwable() {}
copy_throwable(const copy_throwable&) { throw "deal with it"; }