vector_front.h

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#pragma once
 
#include "di/container/vector/constant_vector.h"
#include "di/container/vector/vector_empty.h"
#include "di/container/vector/vector_lookup.h"
#include "di/util/reference_wrapper.h"
#include "di/vocab/optional/prelude.h"
 
namespace di::container::vector {
constexpr auto front(concepts::detail::ConstantVector auto& vector) {
    return lift_bool(!vector::empty(vector)) % [&] {
        return util::ref(vector::lookup(vector, 0));
    };
}
}