c++: no matching function call, particularly it is declared as parameter type unmatching

Question

g++ compiler complains about:

error: no matching function for call to ‘AddressSpace::resolve(ClassOne&, ClassTwo*&, ClassThree&) const’
note: candidates are: bool AddressSpace::resolve(ClassOne&, ClassTwo*, ClassThreer) <near match>

The code causing this error is

void Class::handler(ClassOne& objOne, ClassTwo& objTwo,
        ClassThreer objThree) {

    obj.getAddressSpaceObj().resolve(objOne, objTwo.pointer, objThree);   
}

I digged into the code and found this error is caused by the reference type returned by getOtherObj() . I make it to return a const reference to the AddressSpace object in the class definition, see

const AddressSpace &getAddressSpaceObj(){
   return addressSpace;
}

After I change this definition to return a normal reference,

AddressSpace &getAddressSpaceObj(){
    return addressSpace;
}

the compiler doesn't complain about it any more. I wonder why this error is declared as parameter mismatching error? Why compiler didn't copy content as the parameters of function call but passed them as references?

Answer 1

If resolve does not have a const specifier then you can not call it on a const reference, so that would be consistent with changing it to be being non-const and having it now work. Here is a really trivial example:

#include <iostream>

class A
{
   public:
      void someFuncA() {};
      void someFuncB() const {} ;
} ;

int main()
{
   A
    a1 ;
   const A &aRef = a1 ;

   a1.someFuncA() ;

   // Below won't work because aRef is a const & but someFuncA() not const
   //aRef.someFuncA() ;

   // Below will work since someFuncB() is const
   aRef.someFuncB() ;
}

Just for completeness sake, if you uncomment aRef.someFuncA() then the error you will receive will be similar to this:

19:19: error: no matching function for call to 'A::someFuncA() const'
19:19: note: candidate is:
6:12: note: void A::someFuncA() <near match>