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#include <concepts>
#include <iostream>
template <std::predicate<int> Pred>
void fun(Pred pred, int value)
{
std::cout << pred(value) << '\n';
}
template <typename Container, typename Value>
size_t findIdx(Container const &cont, size_t from, Value const &value)
// requires FindConcept<Container, Value>
{
auto iter = std::find(cont.begin() + from, cont.end(), value);
return iter == cont.end() ? cont.size() : iter - cont.begin();
}
template <typename Container>
concept StdContainer =
requires()
{
typename Container::const_iterator;
typename Container::value_type;
};
// begin(), end() members -> Container::const_iterator
// Container::const_iterator + int -> Container::const_iterator
// Container::const_iterator - Container::const_iterator -> int
// Predicate(Container::value_type)
template <typename Type>
concept Iter =
requires(Type lhs, Type rhs)
{
{ lhs - rhs } -> std::convertible_to<int>; // or: same_as<long int>
{ lhs + 0 } -> std::same_as<Type>;
};
#include <algorithm>
#include <string>
//predicate
template <typename Container, typename Predicate>
concept Find_ifConcept =
std::predicate<Predicate, typename Container::value_type>
and
requires(Container container)
{
{ container.begin() } -> Iter;
{ container.end() } -> Iter;
{ container.size() } -> std::same_as<size_t>;
};
template <typename Container, typename Predicate>
size_t findIdx_if(Container const &cont, size_t from, Predicate const &pred)
requires Find_ifConcept<Container, Predicate>
{
auto iter = std::find_if(cont.begin() + from, cont.end(), pred);
return iter == cont.end() ? cont.size() : iter - cont.begin();
}
int main()
{
std::cout << "Index at " <<
findIdx_if(std::string{ "hello world" }, 0,
[&](int ch)
{
return ch == ' ';
}
) << '\n';
int target = 4;
fun(
[&](int value)
{
return value == target;
},
4
);
}
//=
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