49 lines
1.3 KiB
C++
49 lines
1.3 KiB
C++
// Copyright 2017 Dolphin Emulator Project
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// Licensed under GPLv2+
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// Refer to the license.txt file included.
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#pragma once
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#include <functional>
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#include <utility>
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#include <variant>
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namespace Common
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{
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// A Lazy object holds a value. If a Lazy object is constructed using
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// a function as an argument, that function will be called to compute
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// the value the first time any code tries to access the value.
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template <typename T>
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class Lazy
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{
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public:
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Lazy() : m_value(T()) {}
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Lazy(const std::variant<T, std::function<T()>>& value) : m_value(value) {}
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Lazy(std::variant<T, std::function<T()>>&& value) : m_value(std::move(value)) {}
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const Lazy<T>& operator=(const std::variant<T, std::function<T()>>& value)
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{
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m_value = value;
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return *this;
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}
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const Lazy<T>& operator=(std::variant<T, std::function<T()>>&& value)
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{
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m_value = std::move(value);
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return *this;
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}
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const T& operator*() const { return *ComputeValue(); }
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const T* operator->() const { return ComputeValue(); }
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T& operator*() { return *ComputeValue(); }
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T* operator->() { return ComputeValue(); }
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private:
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T* ComputeValue() const
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{
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if (!std::holds_alternative<T>(m_value))
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m_value = std::get<std::function<T()>>(m_value)();
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return &std::get<T>(m_value);
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}
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mutable std::variant<T, std::function<T()>> m_value;
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};
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}
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