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/* SPDX-License-Identifier: BSL-1.0 OR BSD-3-Clause */
#ifndef MPT_BASE_SPAN_HPP
#define MPT_BASE_SPAN_HPP
#include "mpt/base/detect.hpp"
#include "mpt/base/namespace.hpp"
#include <array>
#if MPT_CXX_AT_LEAST(20)
#include <span>
#else // !C++20
#include <iterator>
#include <limits>
#include <type_traits>
#endif // C++20
#if MPT_CXX_BEFORE(20)
#include <cstddef>
#endif // !C++20
namespace mpt {
inline namespace MPT_INLINE_NS {
#if MPT_CXX_AT_LEAST(20)
using std::dynamic_extent;
using std::span;
#else // !C++20
// Simplified version of gsl::span.
// Non-owning read-only or read-write view into a contiguous block of T
// objects, i.e. equivalent to a (beg,end) or (data,size) tuple.
// Can eventually be replaced without further modifications with a full C++20
// std::span.
inline constexpr std::size_t dynamic_extent = std::numeric_limits<std::size_t>::max();
template <typename T>
class span {
public:
using element_type = T;
using value_type = typename std::remove_cv<T>::type;
using index_type = std::size_t;
using pointer = T *;
using const_pointer = const T *;
using reference = T &;
using const_reference = const T &;
using iterator = pointer;
using difference_type = typename std::iterator_traits<iterator>::difference_type;
private:
T * m_data;
std::size_t m_size;
public:
span() noexcept
: m_data(nullptr)
, m_size(0) {
}
span(pointer beg, pointer end)
: m_data(beg)
, m_size(end - beg) {
}
span(pointer data, index_type size)
: m_data(data)
, m_size(size) {
}
template <std::size_t N>
span(element_type (&arr)[N])
: m_data(arr)
, m_size(N) {
}
template <std::size_t N>
span(std::array<value_type, N> & arr)
: m_data(arr.data())
, m_size(arr.size()) {
}
template <std::size_t N>
span(const std::array<value_type, N> & arr)
: m_data(arr.data())
, m_size(arr.size()) {
}
span(const span & other) noexcept = default;
template <typename U>
span(const span<U> & other)
: m_data(other.data())
, m_size(other.size()) {
}
span & operator=(const span & other) noexcept = default;
iterator begin() const {
return iterator(m_data);
}
iterator end() const {
return iterator(m_data + m_size);
}
reference operator[](index_type index) {
return m_data[index];
}
const_reference operator[](index_type index) const {
return m_data[index];
}
bool operator==(const span & other) const noexcept {
return size() == other.size() && (m_data == other.m_data || std::equal(begin(), end(), other.begin()));
}
bool operator!=(const span & other) const noexcept {
return !(*this == other);
}
pointer data() const noexcept {
return m_data;
}
bool empty() const noexcept {
return size() == 0;
}
index_type size() const noexcept {
return m_size;
}
index_type length() const noexcept {
return size();
}
span subspan(std::size_t offset, std::size_t count = mpt::dynamic_extent) const {
return span(data() + offset, (count == mpt::dynamic_extent) ? (size() - offset) : count);
}
span first(std::size_t count) const {
return span(data(), count);
}
span last(std::size_t count) const {
return span(data() + (size() - count), count);
}
}; // class span
#endif // C++20
template <typename T>
inline span<T> as_span(T * beg, T * end) {
return span<T>(beg, end);
}
template <typename T>
inline span<T> as_span(T * data, std::size_t size) {
return span<T>(data, size);
}
template <typename T, std::size_t N>
inline span<T> as_span(T (&arr)[N]) {
return span<T>(std::begin(arr), std::end(arr));
}
template <typename T, std::size_t N>
inline span<T> as_span(std::array<T, N> & cont) {
return span<T>(cont);
}
template <typename T, std::size_t N>
inline span<const T> as_span(const std::array<T, N> & cont) {
return span<const T>(cont);
}
} // namespace MPT_INLINE_NS
} // namespace mpt
#endif // MPT_BASE_SPAN_HPP
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