Warning for explicitly defaulted special members that end up being deleted ?

Clang Frontend
#1

Hello,

A question popped up on SO today 1: the OP was quite surprised that he could write:

struct X {};

struct Y { 
    Y() = default;
    X& x;
};

And not have any compiler complain about the above code.

Of course, as has been answered, only the instantiation of Y (and thus use of the default constructor) should actually cause an issue; and there is even a clause that the = default can be turned automatically (semantically wise) in a = delete in some cases (such as this one).

Still, even though this is probably very useful for template classes, it is surprising to say the least; and generally being warned earlier is better. Therefore I was wondering if there is a warning in Clang when an explicitly defaulted special member is deleted by the compiler.

I could not find it, if there is (but then there are many warnings to sift through so I might have missed it). Does anyone knows about it ?

– Matthieu

#2

Hello,

A question popped up on SO today [1]: the OP was quite surprised that he could write:

struct X {};

struct Y {
Y() = default;
X& x;
};

And not have any compiler complain about the above code.

Of course, as has been answered, only the instantiation of Y (and thus use of the default constructor) should actually cause an issue; and there is even a clause that the = default can be turned automatically (semantically wise) in a = delete in some cases (such as this one).

Still, even though this is probably very useful for template classes, it is surprising to say the least; and generally being warned earlier is better. Therefore I was wondering if there is a warning in Clang when an explicitly defaulted special member is deleted by the compiler.

I could not find it, if there is (but then there are many warnings to sift through so I might have missed it). Does anyone knows about it ?

Off the cuff I don’t think there is one & it seems like it might be helpful.