Item 32. Preventing Copying
Access specifiers (public, protected, and private) can be used to express and enforce higher-level constraints on how a type may be used.
The most common of these techniques is to disallow copying of an object by declaring its copy operations to be private and not defining them:
class NoCopy {
public:
NoCopy( int );
//...
private:
NoCopy( const NoCopy & ); // copy ctor
NoCopy &operator =( const NoCopy & ); // copy assignment
};
It's necessary to declare the copy constructor and copy assignment operator, since otherwise the compiler would declare them implicitly, as public inline members. By declaring them to be private, we forestall the compiler's meddling and ensure that any use of the operationswhether explicit or implicitwill result in a compile-time error:
void aFunc( NoCopy );
void anotherFunc( const NoCopy & );
NoCopy a( 12 );
NoCopy b( a ); // error! copy ctor
NoCopy c = 12; // error! implicit copy ctor
a = b; // error! copy assignment
aFunc( a ); // error! pass by value with copy ctor
aFunc( 12 ); // error! implicit copy ctor
anotherFunc( a ); // OK, pass by reference
anotherFunc( 12 ); // OK
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