src/common/ityp_span.h

// Copyright 2020 The Dawn Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

#ifndef COMMON_ITYP_SPAN_H_
#define COMMON_ITYP_SPAN_H_

#include "common/TypedInteger.h"
#include "common/UnderlyingType.h"

#include <type_traits>

namespace ityp {

    // ityp::span is a helper class that wraps an unowned packed array of type |Value|.
    // It stores the size and pointer to first element. It has the restriction that
    // indices must be a particular type |Index|. This provides a type-safe way to index
    // raw pointers.
    template <typename Index, typename Value>
    class span {
        using I = UnderlyingType<Index>;

      public:
        constexpr span() : mData(nullptr), mSize(0) {
        }
        constexpr span(Value* data, Index size) : mData(data), mSize(size) {
        }

        constexpr Value& operator[](Index i) const {
            ASSERT(i < mSize);
            return mData[static_cast<I>(i)];
        }

        Value* data() noexcept {
            return mData;
        }

        const Value* data() const noexcept {
            return mData;
        }

        Value* begin() noexcept {
            return mData;
        }

        const Value* begin() const noexcept {
            return mData;
        }

        Value* end() noexcept {
            return mData + static_cast<I>(mSize);
        }

        const Value* end() const noexcept {
            return mData + static_cast<I>(mSize);
        }

        Value& front() {
            ASSERT(mData != nullptr);
            ASSERT(static_cast<I>(mSize) >= 0);
            return *mData;
        }

        const Value& front() const {
            ASSERT(mData != nullptr);
            ASSERT(static_cast<I>(mSize) >= 0);
            return *mData;
        }

        Value& back() {
            ASSERT(mData != nullptr);
            ASSERT(static_cast<I>(mSize) >= 0);
            return *(mData + static_cast<I>(mSize) - 1);
        }

        const Value& back() const {
            ASSERT(mData != nullptr);
            ASSERT(static_cast<I>(mSize) >= 0);
            return *(mData + static_cast<I>(mSize) - 1);
        }

        Index size() const {
            return mSize;
        }

      private:
        Value* mData;
        Index mSize;
    };

}  // namespace ityp

#endif  // COMMON_ITYP_SPAN_H_