span.h

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//
// Copyright 2019 Pixar
//
// Licensed under the Apache License, Version 2.0 (the "Apache License")
// with the following modification; you may not use this file except in
// compliance with the Apache License and the following modification to it:
// Section 6. Trademarks. is deleted and replaced with:
//
// 6. Trademarks. This License does not grant permission to use the trade
//    names, trademarks, service marks, or product names of the Licensor
//    and its affiliates, except as required to comply with Section 4(c) of
//    the License and to reproduce the content of the NOTICE file.
//
// You may obtain a copy of the Apache License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the Apache License with the above modification is
// distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
// KIND, either express or implied. See the Apache License for the specific
// language governing permissions and limitations under the Apache License.
//
#ifndef PXR_BASE_TF_SPAN_H
#define PXR_BASE_TF_SPAN_H


#include "pxr/pxr.h"
#include "pxr/base/tf/api.h"
#include "pxr/base/tf/diagnostic.h"

#include <cstddef>
#include <iterator>
#include <type_traits>


PXR_NAMESPACE_OPEN_SCOPE


template <typename T>
class TfSpan
{
public:
    using element_type = T;
    using value_type = typename std::remove_cv<T>::type;
    using pointer = T*;
    using reference = T&;
    using index_type = std::size_t;
    using difference_type = std::ptrdiff_t;

    using iterator = T*;
    using const_iterator = const T*;
    using reverse_iterator = std::reverse_iterator<iterator>;
    using const_reverse_iterator = std::reverse_iterator<const_iterator>;

    TfSpan() noexcept = default;

    TfSpan(pointer ptr, index_type count)
        : _data(ptr), _size(count)
        {
            TF_DEV_AXIOM(count == 0 || ptr);
        }

    TfSpan(pointer first, pointer last)
        : TfSpan(first, index_type(last-first))
        {
            TF_DEV_AXIOM(last >= first);
        }

    template <class Container>
    TfSpan(Container& cont,
           typename std::enable_if<
               !std::is_const<element_type>::value &&
               std::is_same<typename Container::value_type, value_type
                >::value, Container
           >::type* = 0)
        : _data(cont.data()), _size(cont.size())
        {
            TF_DEV_AXIOM(_size == 0 || _data);
        }

    template <class Container>
    TfSpan(const Container& cont,
           typename std::enable_if<
               std::is_same<typename Container::value_type, value_type
                >::value, Container
           >::type* = 0)
        : _data(cont.data()), _size(cont.size())
        {
            TF_DEV_AXIOM(_size == 0 || _data);
        }

    pointer data() const noexcept { return _data; }

    index_type size() const noexcept { return _size; }

    bool empty() const noexcept { return _size == 0; }

    reference operator[](index_type idx) const {
        TF_DEV_AXIOM(idx < _size);
        return _data[idx];
    }

    reference front() const {
        TF_DEV_AXIOM(!empty());
        return *begin();
    }

    reference back() const {
        TF_DEV_AXIOM(!empty());
        return *(end() - 1);
    }

    iterator begin() const noexcept { return _data; }

    const_iterator cbegin() const noexcept { return _data; }

    iterator end() const noexcept { return _data + _size; }

    const_iterator cend() const noexcept { return _data + _size; }

    reverse_iterator rbegin() const noexcept
        { return reverse_iterator(end()); }

    const_reverse_iterator crbegin() const noexcept 
        { return const_reverse_iterator(cend()); }

    reverse_iterator rend() const noexcept
        { return reverse_iterator(begin()); }

    const_reverse_iterator crend() const noexcept
        { return const_reverse_iterator(cbegin()); }

    TfSpan<T> subspan(difference_type offset, difference_type count=-1) const {
        TF_DEV_AXIOM(offset >= 0 && (index_type)offset < _size);
        if (count == -1) {
            return TfSpan<T>(_data + offset, _size - offset);
        } else {
            TF_DEV_AXIOM(count >= 0);
            TF_DEV_AXIOM(((index_type)offset+(index_type)count) <= _size);
            return TfSpan<T>(_data + offset, count);
        }
    }

    TfSpan<T> first(size_t count) const {
        return subspan(0, count);
    }

    TfSpan<T> last(size_t count) const {
        TF_DEV_AXIOM(_size >= count);
        return TfSpan<T>(end() - count, count);
    }

private:
    pointer _data = nullptr;
    index_type _size = 0;
};


template <typename Container>
TfSpan<typename Container::value_type>
TfMakeSpan(Container& cont)
{
    return TfSpan<typename Container::value_type>(cont);
}


template <typename Container>
TfSpan<const typename Container::value_type>
TfMakeConstSpan(const Container& cont)
{
    return TfSpan<const typename Container::value_type>(cont);
}

PXR_NAMESPACE_CLOSE_SCOPE

#endif // PXR_BASE_TF_SPAN_H