(C++) operator=

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


struct MyClass

{

  MyClass& operator=(const MyClass& rhs)

  {

    //Copy the class members

    return *this;

  }

};

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'.

Handle assignment to self: Identity test


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


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

};

References

Scott Meyers. Effective C++ (3rd edition).ISBN: 0-321-33487-6. Item 10: Have assignment operators return a reference to *this.
Scott Meyers. Effective C++ (3rd edition).ISBN: 0-321-33487-6. Item 11: Handle assignment to self in operator=.
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.'
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'

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