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ppliu · Guest

C++ 98 8.5.3 says:

If the initializer expression is an rvalue, with T2 a class type, and
"cv1 T1" is referencecompatible
with "cv2 T2," the reference is bound in one of the following ways
(the choice is implementationdefined):
- The reference is bound to the object represented by the rvalue (see
3.10) or to a subobject
within
that object.
- A temporary of type "cv1 T2" [sic] is created, and a
constructor is called to copy the entire
rvalue object into the temporary. The reference is bound to the
temporary or to a subobject
within the temporary.93)

The constructor that would be used to make the copy shall be callable
whether or not the copy is
actually done

This disables the code below:

class X
{
X(const X&);
public:
X();
};
void f(X const&);
int main(){
f(X()); //error! X::X(const X&) un-callable
}

But IMO this semantic is absolutely unnecessary.
It disturbs "mojo",making it more complex.

Would you give me some example about the circumstance when the semantic
is necessary?

Thank you in advance.

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