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meta: fix is_compatible/constructible traits (#3020)

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The previous version relied on the existence of an 'iterator' type.

As mentioned in comments, this is not the proper way to do it and
causes issues with certain types (e.g. views from range-v3).

Add a 'is_range' trait that properly detects the return type of
'begin'/'end', and use it in instead.
This commit is contained in:
Théo DELRIEU
2021-10-07 12:32:25 +02:00
committed by GitHub
parent 62f2997b79
commit 80df5e8de6
7 changed files with 321 additions and 132 deletions
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include/nlohmann/detail/macro_scope.hpp
+41 -1
View File
@@ -1,7 +1,8 @@
#pragma once
#include <utility> // pair
#include <utility> // declval, pair
#include <nlohmann/thirdparty/hedley/hedley.hpp>
#include <nlohmann/detail/meta/detected.hpp>
// This file contains all internal macro definitions
// You MUST include macro_unscope.hpp at the end of json.hpp to undef all of them
@@ -292,6 +293,45 @@
inline void to_json(nlohmann::json& nlohmann_json_j, const Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) } \
inline void from_json(const nlohmann::json& nlohmann_json_j, Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM, __VA_ARGS__)) }
// inspired from https://stackoverflow.com/a/26745591
// allows to call any std function as if (e.g. with begin):
// using std::begin; begin(x);
//
// it allows using the detected idiom to retrieve the return type
// of such an expression
#define NLOHMANN_CAN_CALL_STD_FUNC_IMPL(std_name) \
namespace detail { \
using std::std_name; \
\
template<typename... T> \
using result_of_##std_name = decltype(std_name(std::declval<T>()...)); \
} \
\
namespace detail2 { \
struct std_name##_tag \
{ \
}; \
\
template<typename... T> \
std_name##_tag std_name(T&&...); \
\
template<typename... T> \
using result_of_##std_name = decltype(std_name(std::declval<T>()...)); \
\
template<typename... T> \
struct would_call_std_##std_name \
{ \
static constexpr auto const value = ::nlohmann::detail:: \
is_detected_exact<std_name##_tag, result_of_##std_name, T...>::value; \
}; \
} /* namespace detail2 */ \
\
template<typename... T> \
struct would_call_std_##std_name : detail2::would_call_std_##std_name<T...> \
{ \
}
#ifndef JSON_USE_IMPLICIT_CONVERSIONS
#define JSON_USE_IMPLICIT_CONVERSIONS 1
#endif