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Zip like Python in C++! A zip() function for ranges based for loops. See it working: https://godbolt.org/z/6AJdhk
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// Copyright (c) 2019, Conor Williams | |
// Permission to use, copy, modify, and/or distribute this software for any | |
// purpose with or without fee is hereby granted, provided that the above | |
// copyright notice and this permission notice appear in all copies. | |
// Compiling on gcc 9.2 with: -std=c++2a -O3 -fconcepts | |
#ifndef ZIP_CPP | |
#define ZIP_CPP | |
#include <tuple> | |
#include <utility> | |
#include <type_traits> | |
namespace zipper { | |
// **************************************************************************** | |
// * Reusable Tuple Machinery * | |
// **************************************************************************** | |
namespace detail { | |
template <typename> | |
struct is_tuple : std::false_type {}; | |
template <typename... Args> | |
struct is_tuple<std::tuple<Args...>> : std::true_type {}; | |
template <typename... Args> | |
std::tuple<Args...> make_universal_tuple(Args&&... args) { | |
return std::tuple<Args...>{std::forward<Args>(args)...}; | |
} | |
} // namespace detail | |
template <typename T> | |
concept Tuple = detail::is_tuple<std::decay_t<T>>::value; | |
// (tup{a,b,c}, foo) -> tup{foo(a), foo(b), foo(c)} | |
template <Tuple T, typename F> | |
constexpr auto transform(T&& tup, F&& foo) { | |
return std::apply( | |
[foo = std::forward<F>(foo)](auto&&... args) { | |
return detail::make_universal_tuple( | |
foo(std::forward<decltype(args)>(args))...); | |
}, | |
std::forward<T>(tup)); | |
} | |
// Applies foo to every element in tuple | |
template <Tuple T, typename F> | |
constexpr void for_each(T&& tup, F&& foo) { | |
std::apply( | |
[foo = std::forward<F>(foo)](auto&&... args) { | |
/** | |
* (void) required to prevent classes that overload the comma | |
* operator performing extra operations. | |
*/ | |
(((void)foo(std::forward<decltype(args)>(args))), ...); | |
}, | |
std::forward<T>(tup)); | |
} | |
// **************************************************************************** | |
// * Zip Class * | |
// **************************************************************************** | |
namespace detail { | |
template <Tuple A, Tuple B, std::size_t... I> | |
constexpr bool none_equal(A&& a, B&& b, std::index_sequence<I...>) { | |
return (... && (std::get<I>(std::forward<A>(a)) != | |
std::get<I>(std::forward<B>(b)))); | |
} | |
} // namespace detail | |
template <Tuple A, Tuple B> | |
concept same_size = | |
std::tuple_size_v<std::decay_t<A>> == std::tuple_size_v<std::decay_t<B>>; | |
template <Tuple A, Tuple B> | |
requires same_size<A, B> constexpr bool none_equal(A&& a, B&& b) { | |
return detail::none_equal( | |
std::forward<A>(a), std::forward<B>(b), | |
std::make_index_sequence<std::tuple_size_v<std::decay_t<A>>>{}); | |
} | |
template <Tuple T> | |
class ZipIter { | |
private: | |
T iters; | |
public: | |
constexpr explicit ZipIter(T&& tuple) : iters{std::forward<T>(tuple)} {} | |
constexpr bool operator!=(ZipIter const& other) const { | |
return none_equal(iters, other.iters); | |
} | |
ZipIter& operator++() { | |
for_each(iters, [](auto&& x) { x++; }); | |
return *this; | |
} | |
constexpr auto operator*() const { | |
/** | |
* Perfect forwarding of return type allows reference capture for | |
* iterators returning references to members. | |
*/ | |
return transform(iters, [](auto&& x) -> decltype(*x) { return *x; }); | |
} | |
}; | |
template <typename... Args> | |
class Zip { | |
private: | |
std::tuple<Args...> const tup; | |
public: | |
constexpr explicit Zip(Args&&... args) : tup{std::forward<Args>(args)...} {} | |
constexpr auto begin() { | |
return ZipIter{transform(tup, [](auto&& x) { return std::begin(x); })}; | |
} | |
constexpr auto end() { | |
return ZipIter{transform(tup, [](auto&& x) { return std::end(x); })}; | |
} | |
}; | |
} // namespace zipper | |
// Convenience function to make Zip object | |
template <typename... Args> | |
inline constexpr zipper::Zip<Args...> zip(Args&&... args) { | |
return zipper::Zip<Args...>{std::forward<Args>(args)...}; | |
} | |
#endif |
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