mariadb/storage/innobase/include/span.h

/*****************************************************************************

Copyright (c) 2019, MariaDB Corporation.

This program is free software; you can redistribute it and/or modify it under
the terms of the GNU General Public License as published by the Free Software
Foundation; version 2 of the License.

This program is distributed in the hope that it will be useful, but WITHOUT
ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with
this program; if not, write to the Free Software Foundation, Inc.,
51 Franklin Street, Fifth Floor, Boston, MA 02110-1335 USA

*****************************************************************************/

#pragma once

#include <cstddef>
#include <iterator>

namespace st_ {

template <class ElementType> class span {
public:
	typedef ElementType element_type;
	typedef ElementType value_type;
	typedef size_t index_type;
	typedef ptrdiff_t difference_type;
	typedef element_type* pointer;
	typedef const element_type* const_pointer;
	typedef element_type& reference;
	typedef const element_type& const_reference;
	typedef pointer iterator;
	typedef const pointer const_iterator;
	typedef std::reverse_iterator<iterator> reverse_iterator;
	typedef std::reverse_iterator<const_iterator> const_reverse_iterator;

	span() : data_(NULL), size_(0) {}

	span(pointer ptr, index_type count) : data_(ptr), size_(count) {}

	span(pointer first, pointer last) : data_(first), size_(last - first) {}

	template <size_t N> span(element_type (&arr)[N]) : data_(arr), size_(N)
	{
	}

	template <class Container>
	span(Container& cont) : data_(cont.begin()), size_(cont.size())
	{
	}

	template <class Container>
	span(const Container& cont) : data_(cont.begin()), size_(cont.size())
	{
	}

	span(const span& other) : data_(other.data_), size_(other.size_) {}

	~span(){};

	span& operator=(const span& other)
	{
		data_ = other.data_;
		size_ = other.size_;
		return *this;
	}

	template <size_t Count> span<element_type> first() const
	{
		assert(!empty());
		return span(data_, 1);
	}
	template <size_t Count> span<element_type> last() const
	{
		assert(!empty());
		return span(data_ + size() - 1, 1);
	}

	span<element_type> first(index_type count) const
	{
		assert(!empty());
		return span(data_, 1);
	}
	span<element_type> last(index_type count) const
	{
		assert(!empty());
		return span(data_ + size() - 1, 1);
	}
	span<element_type> subspan(index_type offset, index_type count) const
	{
		assert(!empty());
		assert(size() >= offset + count);
		return span(data_ + offset, count);
	}

	index_type size() const { return size_; }
	index_type size_bytes() const { return size_ * sizeof(ElementType); }
	bool empty() const __attribute__((warn_unused_result))
	{
		return size_ == 0;
	}

	reference operator[](index_type idx) const
	{
		assert(size() > idx);
		return data_[idx];
	}
	reference front() const
	{
		assert(!empty());
		return data_[0];
	}
	reference back() const
	{
		assert(!empty());
		return data_[size() - 1];
	}
	pointer data() const
	{
		assert(!empty());
		return data_;
	}

	iterator begin() const { return data_; }
	iterator end() const { return data_ + size_; }
	reverse_iterator rbegin() const
	{
		return std::reverse_iterator<iterator>(std::advance(end(), -1));
	}
	reverse_iterator rend() const
	{
		return std::reverse_iterator<iterator>(
		    std::advance(begin(), -1));
	}

private:
	pointer data_;
	index_type size_;
};

} // namespace st_