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// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
#pragma once
#include <memory>
namespace search::engine {
/**
* A lazy source uses a decoder interface to delay decoding an
* object. Decoding is typically done in another thread as well to
* avoid slowing down the critical path (io event loop).
**/
template <typename T>
class LazySource {
public:
struct Decoder {
virtual std::unique_ptr<T> decode() = 0;
virtual ~Decoder() = default;
};
private:
mutable std::unique_ptr<T> _object;
mutable std::unique_ptr<Decoder> _decoder;
void lazy_decode() const {
if (_decoder && !_object) {
_object = _decoder->decode();
_decoder.reset();
}
}
public:
explicit LazySource(T *object) noexcept : _object(object), _decoder() {}
LazySource(std::unique_ptr<T> object) noexcept : _object(std::move(object)), _decoder() {}
LazySource(std::unique_ptr<Decoder> decoder) noexcept : _object(), _decoder(std::move(decoder)) {}
LazySource(LazySource &&) = default;
~LazySource() {}
LazySource &operator=(LazySource &&) = delete;
LazySource(const LazySource &) = delete;
LazySource &operator=(const LazySource &) = delete;
const T *get() const {
lazy_decode();
return _object.get();
}
const T *operator->() const { return get(); }
std::unique_ptr<T> release() {
lazy_decode();
return std::move(_object);
}
};
}
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