From 41dbd50313b7573190832acace516c6416f72d9b Mon Sep 17 00:00:00 2001 From: Niels Lohmann Date: Wed, 24 Mar 2021 13:27:00 +0100 Subject: [PATCH] :page_facing_up: use code from Google Abseil --- README.md | 2 + include/nlohmann/detail/meta/cpp_future.hpp | 110 +++++++++++++++++--- single_include/nlohmann/json.hpp | 110 +++++++++++++++++--- 3 files changed, 188 insertions(+), 34 deletions(-) diff --git a/README.md b/README.md index d428e4c473..6d0153c091 100644 --- a/README.md +++ b/README.md @@ -1284,6 +1284,8 @@ The class contains a slightly modified version of the Grisu2 algorithm from Flor The class contains a copy of [Hedley](https://nemequ.github.io/hedley/) from Evan Nemerson which is licensed as [CC0-1.0](https://creativecommons.org/publicdomain/zero/1.0/). +The class contains parts of [Google Abseil](https://github.com/abseil/abseil-cpp) which is licensed under the [Apache 2.0 License](https://opensource.org/licenses/Apache-2.0). + ## Contact If you have questions regarding the library, I would like to invite you to [open an issue at GitHub](https://github.com/nlohmann/json/issues/new/choose). Please describe your request, problem, or question as detailed as possible, and also mention the version of the library you are using as well as the version of your compiler and operating system. Opening an issue at GitHub allows other users and contributors to this library to collaborate. For instance, I have little experience with MSVC, and most issues in this regard have been solved by a growing community. If you have a look at the [closed issues](https://github.com/nlohmann/json/issues?q=is%3Aissue+is%3Aclosed), you will see that we react quite timely in most cases. diff --git a/include/nlohmann/detail/meta/cpp_future.hpp b/include/nlohmann/detail/meta/cpp_future.hpp index 4ba1a55714..e24518fafe 100644 --- a/include/nlohmann/detail/meta/cpp_future.hpp +++ b/include/nlohmann/detail/meta/cpp_future.hpp @@ -28,36 +28,112 @@ using std::index_sequence_for; template using enable_if_t = typename std::enable_if::type; -// source: https://stackoverflow.com/a/32223343 -template -struct index_sequence +// The following code is taken from https://github.com/abseil/abseil-cpp/blob/10cb35e459f5ecca5b2ff107635da0bfa41011b4/absl/utility/utility.h +// which is part of Google Abseil (https://github.com/abseil/abseil-cpp), licensed under the Apache License 2.0. + +//// START OF CODE FROM GOOGLE ABSEIL + +// integer_sequence +// +// Class template representing a compile-time integer sequence. An instantiation +// of `integer_sequence` has a sequence of integers encoded in its +// type through its template arguments (which is a common need when +// working with C++11 variadic templates). `absl::integer_sequence` is designed +// to be a drop-in replacement for C++14's `std::integer_sequence`. +// +// Example: +// +// template< class T, T... Ints > +// void user_function(integer_sequence); +// +// int main() +// { +// // user_function's `T` will be deduced to `int` and `Ints...` +// // will be deduced to `0, 1, 2, 3, 4`. +// user_function(make_integer_sequence()); +// } +template +struct integer_sequence { - using type = index_sequence; - using value_type = std::size_t; + using value_type = T; static constexpr std::size_t size() noexcept { return sizeof...(Ints); } }; -template -struct merge_and_renumber; +// index_sequence +// +// A helper template for an `integer_sequence` of `size_t`, +// `absl::index_sequence` is designed to be a drop-in replacement for C++14's +// `std::index_sequence`. +template +using index_sequence = integer_sequence; -template -struct merge_and_renumber, index_sequence> - : index_sequence < I1..., (sizeof...(I1) + I2)... > {}; +namespace utility_internal +{ -template -struct make_index_sequence - : merge_and_renumber < typename make_index_sequence < N / 2 >::type, - typename make_index_sequence < N - N / 2 >::type > {}; +template +struct Extend; -template<> struct make_index_sequence<0> : index_sequence<> {}; -template<> struct make_index_sequence<1> : index_sequence<0> {}; +// Note that SeqSize == sizeof...(Ints). It's passed explicitly for efficiency. +template +struct Extend, SeqSize, 0> +{ + using type = integer_sequence < T, Ints..., (Ints + SeqSize)... >; +}; -template +template +struct Extend, SeqSize, 1> +{ + using type = integer_sequence < T, Ints..., (Ints + SeqSize)..., 2 * SeqSize >; +}; + +// Recursion helper for 'make_integer_sequence'. +// 'Gen::type' is an alias for 'integer_sequence'. +template +struct Gen +{ + using type = + typename Extend < typename Gen < T, N / 2 >::type, N / 2, N % 2 >::type; +}; + +template +struct Gen +{ + using type = integer_sequence; +}; + +} // namespace utility_internal + +// Compile-time sequences of integers + +// make_integer_sequence +// +// This template alias is equivalent to +// `integer_sequence`, and is designed to be a drop-in +// replacement for C++14's `std::make_integer_sequence`. +template +using make_integer_sequence = typename utility_internal::Gen::type; + +// make_index_sequence +// +// This template alias is equivalent to `index_sequence<0, 1, ..., N-1>`, +// and is designed to be a drop-in replacement for C++14's +// `std::make_index_sequence`. +template +using make_index_sequence = make_integer_sequence; + +// index_sequence_for +// +// Converts a typename pack into an index sequence of the same length, and +// is designed to be a drop-in replacement for C++14's +// `std::index_sequence_for()` +template using index_sequence_for = make_index_sequence; +//// END OF CODE FROM GOOGLE ABSEIL + #endif // dispatch utility (taken from ranges-v3) diff --git a/single_include/nlohmann/json.hpp b/single_include/nlohmann/json.hpp index 282f33291f..4493dd6542 100644 --- a/single_include/nlohmann/json.hpp +++ b/single_include/nlohmann/json.hpp @@ -3041,36 +3041,112 @@ using std::index_sequence_for; template using enable_if_t = typename std::enable_if::type; -// source: https://stackoverflow.com/a/32223343 -template -struct index_sequence +// The following code is taken from https://github.com/abseil/abseil-cpp/blob/10cb35e459f5ecca5b2ff107635da0bfa41011b4/absl/utility/utility.h +// which is part of Google Abseil (https://github.com/abseil/abseil-cpp), licensed under the Apache License 2.0. + +//// START OF CODE FROM GOOGLE ABSEIL + +// integer_sequence +// +// Class template representing a compile-time integer sequence. An instantiation +// of `integer_sequence` has a sequence of integers encoded in its +// type through its template arguments (which is a common need when +// working with C++11 variadic templates). `absl::integer_sequence` is designed +// to be a drop-in replacement for C++14's `std::integer_sequence`. +// +// Example: +// +// template< class T, T... Ints > +// void user_function(integer_sequence); +// +// int main() +// { +// // user_function's `T` will be deduced to `int` and `Ints...` +// // will be deduced to `0, 1, 2, 3, 4`. +// user_function(make_integer_sequence()); +// } +template +struct integer_sequence { - using type = index_sequence; - using value_type = std::size_t; + using value_type = T; static constexpr std::size_t size() noexcept { return sizeof...(Ints); } }; -template -struct merge_and_renumber; +// index_sequence +// +// A helper template for an `integer_sequence` of `size_t`, +// `absl::index_sequence` is designed to be a drop-in replacement for C++14's +// `std::index_sequence`. +template +using index_sequence = integer_sequence; + +namespace utility_internal +{ + +template +struct Extend; + +// Note that SeqSize == sizeof...(Ints). It's passed explicitly for efficiency. +template +struct Extend, SeqSize, 0> +{ + using type = integer_sequence < T, Ints..., (Ints + SeqSize)... >; +}; + +template +struct Extend, SeqSize, 1> +{ + using type = integer_sequence < T, Ints..., (Ints + SeqSize)..., 2 * SeqSize >; +}; + +// Recursion helper for 'make_integer_sequence'. +// 'Gen::type' is an alias for 'integer_sequence'. +template +struct Gen +{ + using type = + typename Extend < typename Gen < T, N / 2 >::type, N / 2, N % 2 >::type; +}; + +template +struct Gen +{ + using type = integer_sequence; +}; -template -struct merge_and_renumber, index_sequence> - : index_sequence < I1..., (sizeof...(I1) + I2)... > {}; +} // namespace utility_internal -template -struct make_index_sequence - : merge_and_renumber < typename make_index_sequence < N / 2 >::type, - typename make_index_sequence < N - N / 2 >::type > {}; +// Compile-time sequences of integers -template<> struct make_index_sequence<0> : index_sequence<> {}; -template<> struct make_index_sequence<1> : index_sequence<0> {}; +// make_integer_sequence +// +// This template alias is equivalent to +// `integer_sequence`, and is designed to be a drop-in +// replacement for C++14's `std::make_integer_sequence`. +template +using make_integer_sequence = typename utility_internal::Gen::type; -template +// make_index_sequence +// +// This template alias is equivalent to `index_sequence<0, 1, ..., N-1>`, +// and is designed to be a drop-in replacement for C++14's +// `std::make_index_sequence`. +template +using make_index_sequence = make_integer_sequence; + +// index_sequence_for +// +// Converts a typename pack into an index sequence of the same length, and +// is designed to be a drop-in replacement for C++14's +// `std::index_sequence_for()` +template using index_sequence_for = make_index_sequence; +//// END OF CODE FROM GOOGLE ABSEIL + #endif // dispatch utility (taken from ranges-v3)