(C++) operator=

 

operator= is an operator, that is called the assign operator and assignment operator.

 

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struct MyClass {   MyClass& operator=(const MyClass& rhs)   {     //Copy the class members     return *this;   } };

 

 

 

 

 

Handle assignment to self: Identity test

 

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struct MyClass {   MyClass& operator=(const MyClass& rhs)   {     //'Identity test'     if (this == &rhs) return *this;     //Copy     //...     //Return *this     return *this;   } };

 

 

 

 

 

Handle assignment to self: Copy and swap

 

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struct MyClass {   MyClass& operator=(MyClass tempCopy) //'Copy' (by passing by value)   {     //'Swap'     Swap(tempCopy); //Swaps the data of temp with *this     return *this;   }   void Swap(MyClass& m)   {     //Swap data of m with this     std::swap(mX, m.mX);     //Other data...   }   int mX; //Just to have a member variable };

 

 

 

 

 

Advice

 

• In class design, have assignment operators return a reference to *this [1,3].
• In class design, also handle assignment to self [2,4]. To handle assignment to self there are two techniques: 'identity test' or 'copy and swap'.
• Prefer the {}-initializer syntax for declarations with a named type [7]. Prefer the = syntax for the initialization in declarations using auto [6]
• Reversing the order of the pair of symbols in the operators !=, >= and <= (by writing them as =!, => and =< respectively) is normally a syntax error [5]

 

 

 

 

 

References

 

1. Scott Meyers. Effective C++ (3rd edition).ISBN: 0-321-33487-6. Item 10: Have assignment operators return a reference to *this.
2. Scott Meyers. Effective C++ (3rd edition).ISBN: 0-321-33487-6. Item 11: Handle assignment to self in operator=.
3. Joint Strike Fighter Air Vehicle C++ Coding Standards for the System Development and Demonstration Program. Document Number 2RDU00001 Rev C. December 2005. AV Rule 82: 'An assignment operator shall return a reference to *this.'
4. Joint Strike Fighter Air Vehicle C++ Coding Standards for the System Development and Demonstration Program. Document Number 2RDU00001 Rev C. December 2005. AV Rule 81: 'The assignment operator shall handle self-assignment correctly'
5. Paul Deitel, Harvey Deitel. C++11 for programmers (2nd edition). 2014. ISBN: 978-0-13-343985-4. Chapter 2.4, Common Programming Error 2.2. page 32: 'Reversing the order of the pair of symbols in the operators !=, >= and < (by writing them as =!, => and =< respectively) is normally a syntax error. In some cases, writing != as =! will not be a syntax error, but almost certainly will be a logic error that has an effect at execution time.'
6. Bjarne Stroustrup. The C++ Programming Language (4th edition). 2013. ISBN: 978-0-321-56384-2. Chapter 6.6. Advice, page 169: '[20] Prefer the = syntax for the initialization in declarations using auto'
7. Bjarne Stroustrup. The C++ Programming Language (4th edition). 2013. ISBN: 978-0-321-56384-2. Chapter 6.6. Advice, page 169: '[19] Prefer the {}-initializer syntax for declarations with a named type'