Reference returning method applied on const and non-const object

Question

Consider the following code:

class A{

  my_method(const B& b){
    import_something_from_c(this, b.getC()); // does some sort of copying
  }

}

class B{
  const C& getC() const { return c; };
}

function f(B b){
  b.getC().changeSomething();
}

Since my_method guarantees const, b.getC() must also be const. In f however, I do not guarantee constness and I do want to change the very same b.getC().

Is there some sort of a way to propagate the constness of an object to methods returning references to its members?

juanchopanza · Accepted Answer · 2014-07-17 21:12:41Z

3

You need to provide a non-const overload of getC(). For example

C& getC() { return c; };

answered Jul 17, 2014 at 21:12

juanchopanza

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4 Comments

Michael Over a year ago

Is it that simple? I always thought I could not overload return values. Constness of the value therefore is an exception?

juanchopanza Over a year ago

@Michael This isn't overloading return value, it is overloading on the constness of the member function.

Moby Disk Over a year ago

You are changing more than just the return value since you are also removing the second occurrence of the keyword const. That second const is actually part of the method signature.

M.M Over a year ago

Note, if the methods are complicated then to avoid code duplication you can have the non-const one call the const one, e.g.: C &getC() { return const_cast<C &>( const_cast<C const &>(*this).getC() ); }

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