std::ranges::views::filter, std::ranges::filter_view

template< ranges::input_range V,
std::indirect_unary_predicate<ranges::iterator_t<V>> Pred >
requires ranges::view<V> && std::is_object_v<Pred>
class filter_view
: public ranges::view_interface<filter_view<V, Pred>>

namespace views {
inline constexpr /* unspecified */ filter = /* unspecified */;
}

Call signature

template< ranges::viewable_range R, class Pred >
requires /* see below */
constexpr ranges::view auto filter( R&& r, Pred&& pred );

template< class Pred >
constexpr /* range adaptor closure */ filter( Pred&& pred );

#include <iostream>
#include <ranges>
 
int main()
{
    auto even = [](int i) { return 0 == i % 2; };
    auto square = [](int i) { return i * i; };
 
    for (int i : std::views::iota(0, 6)
               | std::views::filter(even)
               | std::views::transform(square))
        std::cout << i << ' ';
    std::cout << '\n';
}