vector_first.h

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#pragma once
 
#include "di/container/vector/constant_vector.h"
#include "di/container/vector/vector_data.h"
#include "di/container/vector/vector_size.h"
#include "di/types/prelude.h"
#include "di/vocab/optional/prelude.h"
#include "di/vocab/span/fixed_span.h"
#include "di/vocab/span/span_fixed_size.h"
#include "di/vocab/span/span_forward_declaration.h"
 
namespace di::container::vector {
constexpr auto first(concepts::detail::ConstantVector auto& vector, size_t count) {
    return lift_bool(count <= vector::size(vector)) % [&] {
        return vocab::Span { vector::data(vector), count };
    };
}
 
template<size_t count>
constexpr auto first(concepts::detail::ConstantVector auto& vector) {
    return lift_bool(count <= vector::size(vector)) % [&] {
        return vocab::fixed_span<count>(vector::data(vector));
    };
}
}