Why is operator == not automatically synthesized for nested classes in C++
If I try to compile:
class Outer
{
class Inner
{
int t;
};
public:
Inner inner_;
bool operator ==(Outer rightSide);
};
bool Outer::operator ==(Outer rightSide)
{
if (inner_ == rightSide.inner_)
return true;
return false;
}
I get an error:
/home/martin/Projects/Experimentation/Various-build-desktop/../Various/main.cpp:18:
error: no match for ‘operator==’ in ‘((Outer*)this)->Outer::inner_ ==
rightSide.Outer::inner_’
Please, is it just me doing something wrong or is this a property of C++
EDIT:
Oh, I never realized that the operator == is never synthesized, I was so convinced that it is synthesized, that I did not bother to check.
Thank you Parapura Rajkumar!
Comparison operators are never implicitly generated. Only these things are:
If you want to be able to compare your types, you'll have to write your own comparison operators. If you implement them as members, then they should be declared const ; otherwise, it will be impossible to compare constant objects. You might also consider taking arguments as constant references to avoid unnecessary copying; it makes little difference for simple types like these, but can be much more efficient for large or complicated classes. Something like:
bool Outer::operator==(Outer const & rhs) const {
return inner_.t == rhs.inner_.t;
}
or as a non-member function:
bool operator==(Outer const & lhs, Outer const & rhs) {
return lhs.inner_.t == rhs.inner_.t;
}
You didn't define the operator== for class Inner . So your code should be :
class Outer
{
class Inner
{
int t;
public:
bool operator == (Inner inner)
{
return t == inner.t;
}
};
public:
Inner inner_;
bool operator == (Outer rightSide);
};
bool Outer::operator == (Outer rightSide)
{
return inner_ == rightSide.inner_;
}