User-defined conversion function

本文主要是介绍User-defined conversion function，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

https://en.cppreference.com/w/cpp/language/cast_operator

在sp的定义里曾经出现过：

inline explicit operator bool () const { return m_ptr != nullptr; }

这样的代码。operator bool就是User-defined conversion function

template<typename T>
class sp {
public:inline sp() : m_ptr(0) { }sp(T* other);  // NOLINT(implicit)sp(const sp<T>& other);sp(sp<T>&& other);template<typename U> sp(U* other);  // NOLINT(implicit)template<typename U> sp(const sp<U>& other);  // NOLINT(implicit)template<typename U> sp(sp<U>&& other);  // NOLINT(implicit)~sp();// Assignmentsp& operator = (T* other);sp& operator = (const sp<T>& other);sp& operator = (sp<T>&& other);template<typename U> sp& operator = (const sp<U>& other);template<typename U> sp& operator = (sp<U>&& other);template<typename U> sp& operator = (U* other);//! Special optimization for use by ProcessState (and nobody else).void force_set(T* other);// Resetvoid clear();// Accessorsinline T&       operator* () const     { return *m_ptr; }inline T*       operator-> () const    { return m_ptr;  }inline T*       get() const            { return m_ptr; }inline explicit operator bool () const { return m_ptr != nullptr; }// OperatorsCOMPARE(==)COMPARE(!=)COMPARE(>)COMPARE(<)COMPARE(<=)COMPARE(>=)private:    template<typename Y> friend class sp;template<typename Y> friend class wp;void set_pointer(T* ptr);T* m_ptr;
};

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