product.h

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#pragma once
 
#include "di/container/algorithm/fold_left.h"
#include "di/function/multiplies.h"
#include "di/function/pipeline.h"
 
namespace di::container {
namespace detail {
    struct ProductFunction : function::pipeline::EnablePipeline {
        template<concepts::InputIterator Iter, concepts::SentinelFor<Iter> Sent, typename T = meta::IteratorValue<Iter>>
        requires(concepts::IndirectlyBinaryLeftFoldable<function::Multiplies, T, Iter> && requires { T(1); })
        constexpr auto operator()(Iter first, Sent last) const {
            return container::fold_left(util::move(first), util::move(last), T(1), function::multiplies);
        }
 
        template<concepts::InputContainer Con, typename T = meta::ContainerValue<Con>>
        requires(concepts::IndirectlyBinaryLeftFoldable<function::Multiplies, T, meta::ContainerIterator<Con>> &&
                 requires { T(1); })
        constexpr auto operator()(Con&& container) const {
            return (*this)(container::begin(container), container::end(container));
        }
    };
}
 
constexpr inline auto product = detail::ProductFunction {};
}
 
namespace di {
using container::product;
}