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control of defaults: move and copy

• copy assignment
• copy constructor
• move assignment
• move constructor
• destructor

If any move, copy, or destructor is explicitly specified (declared, defined, =default, or =delete) by the user, no move is generated by default. If any move, copy, or destructor is explicitly specified (declared, defined, =default, or =delete) by the user, any undeclared copy operations are generated by default, but this is deprecated, so don‘t rely on that. For example:

 	class X1 { 		X1& operator=(const X1&) = delete;	// Disallow copying 	}; 

 	class X2 { 		X2& operator=(const X2&) = delete; 	}; 

 	class X3 { 		X3& operator=(X3&&) = delete;	// Disallow moving 	}; 

 	class X4 { 		~X4() = delete;	// Disallow destruction 	}; 

I strongly recommend that if you declare one of these five function, you explicitly declare all. For example:

 	template<class T> 	class Handle { 		T* p; 	public: 		Handle(T* pp) : p{pp} {} 		~Handle() { delete p; }		// user-defined destructor: no implicit copy or move   		Handle(Handle&& h) :p{h.p} { h.p=nullptr; }			// transfer ownership 		Handle& operator=(Handle&& h) { delete p; p=h.p; h.p=nullptr; return *this; }	// transfer ownership  		Handle(const Handle&) = delete;		// no copy 		Handle& operator=(const Handle&) = delete;  		// ... 	}; 

See also

• the C++ draft section ???
• [N2326==07-0186] Lawrence Crowl: Defaulted and Deleted Functions.
• [N3174=100164] B. Stroustrup: To move or not to move. An analysis of problems related to generated copy and move operations. Approved.

Stroustrup 谈 C++ 11的新特性