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From: "redi at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug libstdc++/106201] filesystem::directory_iterator is a
 borrowable range?
Date: Tue, 05 Jul 2022 15:31:08 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D106201

--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Reduced to not use concepts:

struct foo
{
  template<typename T, typename =3D decltype(f(*(T*)nullptr))>
    foo(const T&) { }
};

struct bar { };

struct baz
{
  template<typename T> baz(const T&) { }
};

void f(foo&);
void f(baz, ...);

int main()
{
  bar b;
  f(b);
}

G++ goes into infinite recursion, Clang, EDG and MSVC accept it.=