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// Copyright 2024 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef BASE_CONTAINERS_SPAN_OR_SIZE_H_
#define BASE_CONTAINERS_SPAN_OR_SIZE_H_
#include <stddef.h>
#include <variant>
#include "base/containers/span.h"
#include "base/functional/overloaded.h"
#include "base/types/optional_ref.h"
namespace base {
// `SpanOrSize<T>` contains either a `span<T>` or just the size of data. This
// is useful if the data is not retained in some scenarios, but size needs to be
// available in all the scenarios.
template <typename T>
class SpanOrSize {
public:
explicit constexpr SpanOrSize(base::span<T> span) : span_or_size_(span) {}
explicit constexpr SpanOrSize(size_t size) : span_or_size_(size) {}
~SpanOrSize() = default;
// `SpanOrSize` is copyable and movable (just like `span` and `size_t`).
SpanOrSize(const SpanOrSize&) = default;
SpanOrSize& operator=(const SpanOrSize&) = default;
SpanOrSize(SpanOrSize&&) = default;
SpanOrSize& operator=(SpanOrSize&&) = default;
constexpr T* ptr_or_null_if_no_data() const {
return std::visit(Overloaded{
[](const base::span<T>& span) { return span.data(); },
[](size_t size) -> T* { return nullptr; },
},
span_or_size_);
}
constexpr size_t size() const {
return std::visit(Overloaded{
[](const base::span<T>& span) { return span.size(); },
[](size_t size) { return size; },
},
span_or_size_);
}
constexpr optional_ref<const base::span<T>> span() const {
return std::visit(
Overloaded{
[](const base::span<T>& span) {
return optional_ref<const base::span<T>>(span);
},
[](size_t size) { return optional_ref<const base::span<T>>(); },
},
span_or_size_);
}
private:
std::variant<base::span<T>, size_t> span_or_size_;
};
} // namespace base
#endif // BASE_CONTAINERS_SPAN_OR_SIZE_H_
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