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https://github.com/Light-City/CPlusPlusThings.git
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dfe1c933b3
- const README: rewrite the space-saving claim per issue #5 follow-ups (constant-expression const vs #define immediates; which const qualify as constant expressions) - const README: fix the class-section diagnosis per issue #338 (overload resolution picks the const overload; the restriction only surfaces once that overload is removed) - sizeof README: virtual-inheritance result is compiler-dependent (GCC merges vbptr+vfptr -> 16, MSVC keeps them separate -> 32) #246 - static README: new section on internal linkage / access restriction with anonymous-namespace comparison #142 - 10-day practice: full problem list table + fixed day links #136 - new design_pattern/singleton/singleton_default.hpp: reusable thread-safe CRTP singleton template, compile+concurrency tested #303
59 lines
1.5 KiB
C++
59 lines
1.5 KiB
C++
/**
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* @file singleton_default.hpp
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* @brief 可复用的线程安全单例模板基类（CRTP）
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* 受 issue #303 启发：https://github.com/Light-City/CPlusPlusThings/issues/303
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* 参考 boost::container::singleton_default 的思路。
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*
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* 用法：
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* class MyConfig : public SingletonDefault<MyConfig> {
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* friend class SingletonDefault<MyConfig>;
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* private:
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* MyConfig() = default; // 构造私有，交由基类创建
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* public:
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* int value = 42;
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* };
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* MyConfig::instance().value = 1;
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*
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* 编译：g++ -std=c++11 main.cpp
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* @author 光城
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* @version v1
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* @date 2026-10
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*/
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#pragma once
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#include <mutex>
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template <class T>
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class SingletonDefault {
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public:
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SingletonDefault(const SingletonDefault&) = delete;
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SingletonDefault& operator=(const SingletonDefault&) = delete;
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static T& instance() {
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// C++11 起，局部静态变量的初始化由标准保证线程安全（"magic statics"）
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static T inst;
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return inst;
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}
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protected:
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SingletonDefault() = default;
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~SingletonDefault() = default;
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};
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/**
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* 若需要 C++03 或对 magic statics 不放心的环境，可用 call_once 版本：
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*
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* template <class T>
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* class SingletonDefaultOnce {
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* public:
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* static T& instance() {
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* std::call_once(once_, [] { inst_.reset(new T); });
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* return *inst_;
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* }
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* private:
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* static std::once_flag once_;
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* static std::unique_ptr<T> inst_;
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* };
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*/
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