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concept.cpp
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concept.cpp
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/*
* Concept is a feature introduced in C++20.
*/
#include <iostream>
#include <concepts>
#include <ranges>
#include <iterator>
#include <initializer_list>
template<typename T>
using value_type_v = typename T::value_type;
template<typename T>
using iterator_type_v = typename T::iterator;
template<typename S>
concept Sequence = requires(S a) {
typename value_type_v<S>;
typename iterator_type_v<S>;
{begin(a)} -> std::same_as<iterator_type_v<S>>;
{end(a)} -> std::same_as<iterator_type_v<S>>;
requires std::same_as<
value_type_v<S>,
value_type_v<std::iterator_traits<iterator_type_v<S>>>>;
requires std::input_iterator<iterator_type_v<S>>;
};
template<typename T, typename U = T>
concept Arithmetic = requires(T a, U b) {
{a + b} -> std::same_as<T>;
{a - b} -> std::same_as<T>;
{a * b} -> std::same_as<T>;
{a / b} -> std::same_as<T>;
};
template<Sequence Seq, Arithmetic<value_type_v<Seq>> Num>
Num sum(Seq s, Num v)
{
for (const auto& x : s)
v += x;
return v;
}
template<Arithmetic Num>
Num sum(const std::initializer_list<Num>& il, Num v)
{
for (const auto& x : il)
v += x;
return v;
}
int main()
{
std::cout << sum({1,2,3,4}, 0);
}