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From: "kentsangkm at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug c++/106619] New: Inconsistent __PRETTY_FUNCTION__ output
Date: Mon, 15 Aug 2022 08:05:37 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D106619

            Bug ID: 106619
           Summary: Inconsistent __PRETTY_FUNCTION__ output
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: kentsangkm at gmail dot com
  Target Milestone: ---

Created attachment 53456
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=3D53456&action=3Dedit
example code

The __PRETTY_FUNCTION__ macro does print the function name as well as the
template arguments (if any), but the output is inconsistent and depends on =
the
declaration sequence.

// any templated typed with optional parameter(s)
template<typename T, typename U =3D std::conditional_t<std::is_void_v<T>, v=
oid,
T>>
struct Foo
{
};

template<typename T>
struct Container
{
    void get() const{
        std::cout << typeid(T).name() << "  "<< __PRETTY_FUNCTION__ <<
std::endl;
    }
};

int main()
{
    Container<Foo<int, int>> b;
    b.get();

    Container<Foo<int>> a;
    a.get();
}


Output:
3FooIiiE  void Container<T>::get() const [with T =3D Foo<int, int>]
3FooIiiE  void Container<T>::get() const [with T =3D Foo<int, int>]



If we swap the declaration of a and b, the output becomes:
3FooIiiE  void Container<T>::get() const [with T =3D Foo<int>]
3FooIiiE  void Container<T>::get() const [with T =3D Foo<int>]


in contrast, the typeid is very consistent on both cases, but it is not an
constexpr function



Clang does not have such issue, as it always expends the optional arguments=
 and
output Foo<int, int> always


Here is a short link for godbolt
https://godbolt.org/z/vfTnz5bEb

the same code piece is also be enclosed=