https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87063
Bug ID: 87063
Summary: Const subobject with const assignment operator, but
operator anyway deleted
Product: gcc
Version: 9.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: wandersys at aim dot com
Target Milestone: ---
Hello!
Here is an example:
class bar
{
public:
bar() {}
bar const & operator=(bar const &) const
{
return *this;
}
};
class foo
{
bar const v;
};
int main()
{
foo a;
a = foo();
}
Here are the relevant points of the standard:
------
7) A defaulted copy/move assignment operator for class X is defined as deleted
if X has:
(7.1) a variant member with a non-trivial corresponding assignment operator and
X is a union-like class, or
(7.2) a non-static data member of const non-class type (or array thereof), or
(7.3) a non-static data member of reference type, or
(7.4) a direct non-static data member of class type M (or array thereof) or a
direct base class M that cannot be copied/moved because overload resolution, as
applied to find M's corresponding assignment operator, results in an ambiguity
or a function that is deleted or inaccessible from the defaulted assignment
operator.
------
Thus, the operator can be `deleted` because of clause 7.4, which relies on
overload resolution rules. If we remove the const qualification from the
assignment operator, then this clause will be executed, since we cannot allow
assignment overloading for a constant object (in this way). Currently, by
adding the const-qualification of the operator, I hope to disable this rule
because overload resolution becomes possible. However, the compiler forbids me.
This code works fine in vc++ and clang, but not in gcc.
