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494be1c445
json/include/nlohmann/detail/output/fancy_serializer.hpp
Evan Driscoll 494be1c445 Refactor: rename the register_style overloads 
I really really wanted to name these the same and overload them,
but I couldn't get the metaprogramming to work right. Here's a
comment I wrote that describes the problems and what I *planned*
to do:

// What we want is the register_style overloads below. I chose to
// keep them with the same name. But there are two problems with
// that. First, because I need to wrap them in a std::function
// when promoting to two arguments, I want to make register_style
// themselves take the function parameter by a template argument
// so it doesn't get type-erased "twice" (with two virtual
// calls). But then that means that both versions would have the
// generic signature "template <typename Predicate>
// ... (Predicate, style)" and that would lead to ambiguous calls.
//
// The second problem is that ever if you keep the first parameter
// a std::function, because 'json_pointer' is implicitly
// convertible to a 'json', if you rely on the implicit conversion
// to std::function then you'd get an ambugious call.
//
// So what we want is, using Concept terms:
//
//    template <JsonCallable Predicate> ... (Predicate, style)
//    template <JsonPointerCallable Predicate> ... (Predicate, style)
//
// where JsonCallable is additionally *not*
// JsonPointerCallable. The following is my attempt to get that.

I then wrote some code that is similar to this:

    #include <functional>

    struct Main {};
    struct Secondary { Secondary(Main); };

    // http://en.cppreference.com/w/cpp/types/void_t
    template<typename... Ts> struct make_void { typedef void type;};
    template<typename... Ts> using void_t = typename make_void<Ts...>::type;

    template <typename, typename = void>
    struct can_be_called_with_main : std::false_type { };

    template <typename T>
    struct can_be_called_with_main<
        T,
        void_t<decltype(std::declval<T>()(std::declval<Main>()))>
    >: std::true_type { };

    template <typename, typename = void>
    struct can_be_called_with_secondary : std::false_type { };

    template <typename T>
    struct can_be_called_with_secondary<
        T,
        void_t<decltype(std::declval<T>()(std::declval<Secondary>()))>
    >: std::true_type { };

    template <typename Functor>
    auto
    func(Functor f)
    -> typename std::enable_if<can_be_called_with_main<Functor>::value, int>::type
    {
        return 0;
    }

    template <typename Functor>
    auto
    func(Functor f)
    -> typename std::enable_if<
            can_be_called_with_secondary<Functor>::value
            && !can_be_called_with_main<Functor>::value
            , int>::type
    {
        return 0;
    }

    auto x1 = func([] (Main) {});
    auto x2 = func([] (Secondary) {});

where Main is like 'json' and Secondary like 'json_pointer'.

Problem is it doesn't work -- in the SFIANE context, it looks like
predicates of both `bool (json)` and `bool (json_pointer)` are callable
with both json and json_pointer objects.

In the case of `bool (json)` being called with a 'json_pointer', that
is via the implicit conversion discussed in the comment above. In the
caes of `bool (json_pointer)` being called with a `json`, my guess
as to what is going on is that `json` provides an implicit to-anything
conversion, which uses a `from_json` function. However, that isn't
implemented in a SFIANE-friendly way -- when you try to actually make
that conversion, there's a static_assert failure.

An alternative approach would be to extract the first argument to
the provided predicate via some technique like those described in
https://functionalcpp.wordpress.com/2013/08/05/function-traits/,
and then is_same them vs json and json_pointer.
2018-06-04 22:28:58 -05:00

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#pragma once
#include <algorithm> // reverse, remove, fill, find, none_of
#include <array> // array
#include <cassert> // assert
#include <ciso646> // and, or
#include <clocale> // localeconv, lconv
#include <cmath> // labs, isfinite, isnan, signbit
#include <cstddef> // size_t, ptrdiff_t
#include <cstdint> // uint8_t
#include <cstdio> // snprintf
#include <limits> // numeric_limits
#include <string> // string
#include <type_traits> // is_same
#include <map>
#include <sstream>
#include <functional>
#include <vector>
#include <nlohmann/detail/exceptions.hpp>
#include <nlohmann/detail/conversions/to_chars.hpp>
#include <nlohmann/detail/macro_scope.hpp>
#include <nlohmann/detail/meta.hpp>
#include <nlohmann/detail/output/output_adapters.hpp>
#include <nlohmann/detail/value_t.hpp>
#include <nlohmann/detail/output/primitive_serializer.hpp>
#include <nlohmann/detail/json_pointer.hpp>
namespace nlohmann
{
struct fancy_serializer_style
{
unsigned int indent_step = 4;
char indent_char = ' ';
unsigned int depth_limit = std::numeric_limits<unsigned>::max();
unsigned int strings_maximum_length = 0;
bool space_after_colon = false;
bool space_after_comma = false;
bool multiline = false;
fancy_serializer_style() = default;
fancy_serializer_style(bool s_colon, bool s_comma, bool ml)
: space_after_colon(s_colon), space_after_comma(s_comma), multiline(ml)
{}
static const fancy_serializer_style preset_compact;
static const fancy_serializer_style preset_one_line;
static const fancy_serializer_style preset_multiline;
};
const fancy_serializer_style fancy_serializer_style::preset_compact(false, false, false);
const fancy_serializer_style fancy_serializer_style::preset_one_line(true, true, false);
const fancy_serializer_style fancy_serializer_style::preset_multiline(true, true, true);
template<typename BasicJsonType>
class basic_fancy_serializer_stylizer
{
public:
using string_t = typename BasicJsonType::string_t;
using json_pointer_t = json_pointer<BasicJsonType>;
using json_matcher_predicate = std::function<bool (const BasicJsonType&)>;
using context_matcher_predicate = std::function<bool (const json_pointer_t&)>;
using matcher_predicate = std::function<bool (const json_pointer_t&, const BasicJsonType&)>;
basic_fancy_serializer_stylizer(fancy_serializer_style const& ds)
: default_style(ds)
{}
basic_fancy_serializer_stylizer() = default;
public:
const fancy_serializer_style& get_default_style() const
{
return default_style;
}
fancy_serializer_style& get_default_style()
{
return default_style;
}
const fancy_serializer_style* get_new_style_or_active(
const json_pointer_t& pointer,
const json& j,
const fancy_serializer_style* active_style) const
{
for (auto const& pair : styles)
{
if (pair.first(pointer, j))
{
return &pair.second;
}
}
return active_style;
}
fancy_serializer_style& register_style(
matcher_predicate p,
fancy_serializer_style style = fancy_serializer_style())
{
styles.emplace_back(p, style);
return styles.back().second;
}
template <typename Predicate>
fancy_serializer_style& register_style_object_pred(
Predicate p,
fancy_serializer_style style = fancy_serializer_style())
{
auto wrapper = [p](const json_pointer_t&, const BasicJsonType & j)
{
return p(j);
};
styles.emplace_back(wrapper, style);
return styles.back().second;
}
template <typename Predicate>
fancy_serializer_style& register_style_context_pred(
Predicate p,
fancy_serializer_style style = fancy_serializer_style())
{
auto wrapper = [p](const json_pointer_t& c, const BasicJsonType&)
{
return p(c);
};
styles.emplace_back(wrapper, style);
return styles.back().second;
}
fancy_serializer_style& register_key_matcher_style(
string_t str,
fancy_serializer_style style = fancy_serializer_style())
{
return register_style_context_pred([str](const json_pointer_t& pointer)
{
return (pointer.cbegin() != pointer.cend())
&& (*pointer.crbegin() == str);
},
style);
}
fancy_serializer_style& last_registered_style()
{
return styles.back().second;
}
private:
fancy_serializer_style default_style;
std::vector<std::pair<matcher_predicate, fancy_serializer_style>> styles;
};
namespace detail
{
///////////////////
// serialization //
///////////////////
template<typename BasicJsonType>
class fancy_serializer
{
using stylizer_t = basic_fancy_serializer_stylizer<BasicJsonType>;
using primitive_serializer_t = primitive_serializer<BasicJsonType>;
using string_t = typename BasicJsonType::string_t;
using number_float_t = typename BasicJsonType::number_float_t;
using number_integer_t = typename BasicJsonType::number_integer_t;
using number_unsigned_t = typename BasicJsonType::number_unsigned_t;
using json_pointer_t = json_pointer<BasicJsonType>;
static constexpr uint8_t UTF8_ACCEPT = 0;
static constexpr uint8_t UTF8_REJECT = 1;
public:
/*!
@param[in] s output stream to serialize to
@param[in] ichar indentation character to use
*/
fancy_serializer(output_adapter_t<char> s,
const stylizer_t& st)
: o(std::move(s)), stylizer(st),
indent_string(512, st.get_default_style().indent_char)
{}
// delete because of pointer members
fancy_serializer(const fancy_serializer&) = delete;
fancy_serializer& operator=(const fancy_serializer&) = delete;
void dump(const BasicJsonType& val, const bool ensure_ascii)
{
dump(val, ensure_ascii, 0, &stylizer.get_default_style(), json_pointer_t());
}
private:
/*!
@brief internal implementation of the serialization function
This function is called by the public member function dump and organizes
the serialization internally. The indentation level is propagated as
additional parameter. In case of arrays and objects, the function is
called recursively.
- strings and object keys are escaped using `escape_string()`
- integer numbers are converted implicitly via `operator<<`
- floating-point numbers are converted to a string using `"%g"` format
@param[in] val value to serialize
@param[in] pretty_print whether the output shall be pretty-printed
@param[in] depth the current recursive depth
*/
void dump(const BasicJsonType& val,
const bool ensure_ascii,
const unsigned int depth,
const fancy_serializer_style* active_style,
const json_pointer_t& context)
{
active_style = stylizer.get_new_style_or_active(context, val, active_style);
switch (val.m_type)
{
case value_t::object:
{
dump_object(val, ensure_ascii, depth, active_style, context);
return;
}
case value_t::array:
{
dump_array(val, ensure_ascii, depth, active_style, context);
return;
}
case value_t::string:
{
dump_string(*val.m_value.string, ensure_ascii, active_style);
return;
}
case value_t::boolean:
{
if (val.m_value.boolean)
{
o->write_characters("true", 4);
}
else
{
o->write_characters("false", 5);
}
return;
}
case value_t::number_integer:
{
prim_serializer.dump_integer(*o, val.m_value.number_integer);
return;
}
case value_t::number_unsigned:
{
prim_serializer.dump_integer(*o, val.m_value.number_unsigned);
return;
}
case value_t::number_float:
{
prim_serializer.dump_float(*o, val.m_value.number_float);
return;
}
case value_t::discarded:
{
o->write_characters("<discarded>", 11);
return;
}
case value_t::null:
{
o->write_characters("null", 4);
return;
}
}
}
private:
template <typename Iterator>
void dump_object_key_value(
Iterator i, bool ensure_ascii, unsigned int depth,
const fancy_serializer_style* active_style,
const json_pointer_t& context)
{
const auto new_indent = (depth + 1) * active_style->indent_step * active_style->multiline;
const int newline_len = active_style->space_after_colon;
o->write_characters(indent_string.c_str(), new_indent);
o->write_character('\"');
prim_serializer.dump_escaped(*o, i->first, ensure_ascii);
o->write_characters("\": ", 2 + newline_len);
dump(i->second, ensure_ascii, depth + 1, active_style, context.appended(i->first));
}
void dump_object(const BasicJsonType& val,
bool ensure_ascii,
unsigned int depth,
const fancy_serializer_style* active_style,
const json_pointer_t& context)
{
if (val.m_value.object->empty())
{
o->write_characters("{}", 2);
return;
}
else if (depth >= active_style->depth_limit)
{
o->write_characters("{...}", 5);
return;
}
// variable to hold indentation for recursive calls
const auto old_indent = depth * active_style->indent_step * active_style->multiline;
const auto new_indent = (depth + 1) * active_style->indent_step * active_style->multiline;
if (JSON_UNLIKELY(indent_string.size() < new_indent))
{
indent_string.resize(indent_string.size() * 2, active_style->indent_char);
}
const int newline_len = (active_style->multiline ? 1 : 0);
o->write_characters("{\n", 1 + newline_len);
// first n-1 elements
auto i = val.m_value.object->cbegin();
for (std::size_t cnt = 0; cnt < val.m_value.object->size() - 1; ++cnt, ++i)
{
dump_object_key_value(i, ensure_ascii, depth, active_style, context);
o->write_characters(",\n", 1 + newline_len);
}
// last element
assert(i != val.m_value.object->cend());
assert(std::next(i) == val.m_value.object->cend());
dump_object_key_value(i, ensure_ascii, depth, active_style, context);
o->write_characters("\n", newline_len);
o->write_characters(indent_string.c_str(), old_indent);
o->write_character('}');
}
void dump_array(const BasicJsonType& val,
bool ensure_ascii,
unsigned int depth,
const fancy_serializer_style* active_style,
const json_pointer_t& context)
{
if (val.m_value.array->empty())
{
o->write_characters("[]", 2);
return;
}
else if (depth >= active_style->depth_limit)
{
o->write_characters("[...]", 5);
return;
}
// variable to hold indentation for recursive calls
const auto old_indent = depth * active_style->indent_step * active_style->multiline;;
const auto new_indent = (depth + 1) * active_style->indent_step * active_style->multiline;;
if (JSON_UNLIKELY(indent_string.size() < new_indent))
{
indent_string.resize(indent_string.size() * 2, active_style->indent_char);
}
const int newline_len = (active_style->multiline ? 1 : 0);
using pair = std::pair<const char*, int>;
auto comma_string =
active_style->multiline ? pair(",\n", 2) :
active_style->space_after_comma ? pair(", ", 2) :
pair(",", 1);
o->write_characters("[\n", 1 + newline_len);
// first n-1 elements
for (auto i = val.m_value.array->cbegin();
i != val.m_value.array->cend() - 1; ++i)
{
o->write_characters(indent_string.c_str(), new_indent);
dump(*i, ensure_ascii, depth + 1, active_style,
context.appended(i - val.m_value.array->cbegin()));
o->write_characters(comma_string.first, comma_string.second);
}
// last element
assert(not val.m_value.array->empty());
o->write_characters(indent_string.c_str(), new_indent);
dump(val.m_value.array->back(), ensure_ascii, depth + 1, active_style,
context.appended(val.m_value.array->size()));
o->write_characters("\n", newline_len);
o->write_characters(indent_string.c_str(), old_indent);
o->write_character(']');
}
void dump_string(const string_t& str, bool ensure_ascii,
const fancy_serializer_style* active_style)
{
o->write_character('\"');
if (active_style->strings_maximum_length == 0)
{
prim_serializer.dump_escaped(*o, str, ensure_ascii);
}
else
{
std::stringstream ss;
nlohmann::detail::output_adapter<char> o_string(ss);
nlohmann::detail::output_adapter_t<char> oo_string = o_string;
prim_serializer.dump_escaped(*oo_string, str, ensure_ascii);
std::string full_str = ss.str();
if (full_str.size() <= active_style->strings_maximum_length)
{
o->write_characters(full_str.c_str(), full_str.size());
}
else
{
const unsigned start_len = [](unsigned int maxl)
{
if (maxl <= 3)
{
// There is only room for the ellipsis,
// no characters from the string
return 0u;
}
else if (maxl <= 5)
{
// With four allowed characters, we add in the
// first from the string. With five, we add in
// the *last* instead, so still just one at
// the start.
return 1u;
}
else
{
// We subtract three for the ellipsis
// and one for the last character.
return maxl - 4;
}
}(active_style->strings_maximum_length);
const unsigned end_len =
active_style->strings_maximum_length >= 5 ? 1 : 0;
const unsigned ellipsis_length =
active_style->strings_maximum_length >= 3
? 3
: active_style->strings_maximum_length;
o->write_characters(full_str.c_str(), start_len);
o->write_characters("...", ellipsis_length);
o->write_characters(full_str.c_str() + str.size() - end_len, end_len);
}
}
o->write_character('\"');
}
private:
/// the output of the fancy_serializer
output_adapter_t<char> o = nullptr;
/// Used for serializing "base" objects. Strings are sort of
/// counted in this, but not completely.
primitive_serializer_t prim_serializer;
/// the indentation string
string_t indent_string;
/// Output style
const stylizer_t stylizer;
};
}
template<typename BasicJsonType>
std::ostream& fancy_dump(std::ostream& o, const BasicJsonType& j,
basic_fancy_serializer_stylizer<BasicJsonType> const& stylizer)
{
// do the actual serialization
detail::fancy_serializer<BasicJsonType> s(detail::output_adapter<char>(o), stylizer);
s.dump(j, false);
return o;
}
template<typename BasicJsonType>
std::ostream& fancy_dump(std::ostream& o, const BasicJsonType& j,
fancy_serializer_style style)
{
basic_fancy_serializer_stylizer<BasicJsonType> stylizer(style);
return fancy_dump(o, j, stylizer);
}
}
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