premiere-libtorrent/include/libtorrent/span.hpp

/*

Copyright (c) 2016, Arvid Norberg
All rights reserved.

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modification, are permitted provided that the following conditions
are met:

    * Redistributions of source code must retain the above copyright
      notice, this list of conditions and the following disclaimer.
    * Redistributions in binary form must reproduce the above copyright
      notice, this list of conditions and the following disclaimer in
      the documentation and/or other materials provided with the distribution.
    * Neither the name of the author nor the names of its
      contributors may be used to endorse or promote products derived
      from this software without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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*/

#ifndef TORRENT_SPAN_HPP_INCLUDED
#define TORRENT_SPAN_HPP_INCLUDED

#include <array>
#include <type_traits>
#include "libtorrent/assert.hpp"

namespace libtorrent {

namespace aux {

	template <typename From, typename To>
	struct compatible_type
	{
		// conversions that are OK
		// int -> int
		// int const -> int const
		// int -> int const
		// int -> int volatile
		// int -> int const volatile
		// int volatile -> int const volatile
		// int const -> int const volatile

		static const bool value = std::is_same<From, To>::value
			|| std::is_same<From, typename std::remove_const<To>::type>::value
			|| std::is_same<From, typename std::remove_volatile<To>::type>::value
			|| std::is_same<From, typename std::remove_cv<To>::type>::value
			;
	};
}

	template <typename T>
	struct span
	{
		span() : m_ptr(nullptr), m_len(0) {}

		template <typename U, typename
			= typename std::enable_if<aux::compatible_type<U, T>::value>::type>
		span(span<U> const& v) // NOLINT
			: m_ptr(v.data()), m_len(v.size()) {}

		span(T& p) : m_ptr(&p), m_len(1) {} // NOLINT
		span(T* p, std::size_t const l) : m_ptr(p), m_len(l) {} // NOLINT

		template <typename U, std::size_t N>
		span(std::array<U, N>& arr) // NOLINT
			: m_ptr(arr.data()), m_len(arr.size()) {}

		template <typename U, std::size_t N>
		span(U (&arr)[N]) // NOLINT
			: m_ptr(&arr[0]), m_len(N) {}

		// anything with a .data() member function is considered a container
		// but only if the value type is compatible with T
		template <typename Cont
			, typename U = typename std::remove_reference<decltype(*std::declval<Cont>().data())>::type
			, typename = typename std::enable_if<aux::compatible_type<U, T>::value>::type>
		span(Cont& c) // NOLINT
			: m_ptr(c.data()), m_len(c.size()) {}

		std::size_t size() const { return m_len; }
		bool empty() const { return m_len == 0; }
		T* data() const { return m_ptr; }

		using iterator = T*;
		using reverse_iterator = std::reverse_iterator<T*>;

		T* begin() const { return m_ptr; }
		T* end() const { return m_ptr + m_len; }
		reverse_iterator rbegin() const { return reverse_iterator(end()); }
		reverse_iterator rend() const { return reverse_iterator(begin()); }

		T& front() const { TORRENT_ASSERT(m_len > 0); return m_ptr[0]; }
		T& back() const { TORRENT_ASSERT(m_len > 0); return m_ptr[m_len - 1]; }

		span<T> first(std::size_t const n) const
		{
			TORRENT_ASSERT(size() >= n);
			return { data(), n };
		}

		span<T> last(std::size_t const n) const
		{
			TORRENT_ASSERT(size() >= n);
			return { data() + size() - n, n };
		}

		span<T> subspan(std::size_t const offset) const
		{
			TORRENT_ASSERT(size() >= offset);
			return { data() + offset, size() - offset };
		}

		span<T> subspan(std::size_t const offset, std::size_t const count) const
		{
			TORRENT_ASSERT(size() >= offset);
			TORRENT_ASSERT(size() >= offset + count);
			return { data() + offset, count };
		}

		T& operator[](std::size_t const idx) const
		{
			TORRENT_ASSERT(idx < m_len);
			return m_ptr[idx];
		}

	private:
		T* m_ptr;
		std::size_t m_len;
	};

	template <class T, class U>
	inline bool operator==(span<T> const& lhs, span<U> const& rhs)
	{
		return  lhs.size()  == rhs.size()
			&& (lhs.begin() == rhs.begin() || std::equal(lhs.begin(), lhs.end(), rhs.begin()));
	}

}

#endif // TORRENT_SPAN_HPP_INCLUDED