wehub-resource-sync
55 lines
1.2 KiB
C++
55 lines
1.2 KiB
C++
/**
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* Copyright (c) 2019 by Contributors
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* @file dgl/lazy.h
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* @brief Lazy object that will be materialized only when being queried.
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*/
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#ifndef DGL_LAZY_H_
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#define DGL_LAZY_H_
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#include <memory>
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namespace dgl {
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/**
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* @brief Lazy object that will be materialized only when being queried.
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*
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* The object should be immutable -- no mutation once materialized.
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* The object is currently not threaad safe.
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*/
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template <typename T>
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class Lazy {
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public:
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/** @brief default constructor to construct a lazy object */
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Lazy() {}
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/**
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* @brief constructor to construct an object with given value (non-lazy case)
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*/
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explicit Lazy(const T& val) : ptr_(new T(val)) {}
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/** @brief destructor */
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~Lazy() = default;
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/**
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* @brief Get the value of this object. If the object has not been
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* instantiated, using the provided function to create it.
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* @param fn The creator function.
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* @return the object value.
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*/
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template <typename Fn>
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const T& Get(Fn fn) {
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if (!ptr_) {
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ptr_.reset(new T(fn()));
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}
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return *ptr_;
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}
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private:
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/** @brief the internal data pointer */
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std::shared_ptr<T> ptr_{nullptr};
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};
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} // namespace dgl
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#endif // DGL_LAZY_H_
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