[Bug c++/94799] New: [7.2+ Regression] Calling a member template function fails
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94799
Bug ID: 94799
Summary: [7.2+ Regression] Calling a member template function
fails
Product: gcc
Version: 9.3.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: ojman101 at protonmail dot com
Target Milestone: ---
>From gcc version 7.2 and upwards this c++ code, using a member template
function look-up, fails to compile:
template
struct A {
int a() {
return 42;
}
};
template
struct B {
int b(A *p) {
return p->template A::a();
}
};
int main() {
A a;
B b;
return b.b(&a);
}
On gcc version 9.3.0 (Gentoo 9.3.0 p2), this output is generated:
main.cc: In member function 'int B::b(A*)':
main.cc:11:32: error: expected ';' before '::' token
11 | return p->template A::a();
|^~
|;
main.cc:11:34: error: '::a' has not been declared
11 | return p->template A::a();
| ^
main.cc: In instantiation of 'int B::b(A*) [with T = int]':
main.cc:18:18: required from here
main.cc:11:28: error: 'A' is not a member template function
11 | return p->template A::a();
|^~~~
This code successfully compiles on new versions of clang, icc and msvc as well
as gcc versions before 7.2.
[Bug c++/95066] New: [C++ 20] Incorrect valid compilation with a conditional explicit
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95066
Bug ID: 95066
Summary: [C++ 20] Incorrect valid compilation with a
conditional explicit
Product: gcc
Version: 9.3.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: ojman101 at protonmail dot com
Target Milestone: ---
The code below is invalid C++, the line "Foo b = a;" should fail to
compile as implicitly casting is made illegal by the conditional explicit using
the "IsSafelyCastable" predicate.
#include
template
class IsSafelyCastable : public std::false_type {};
template <>
class IsSafelyCastable : public std::true_type {};
template
struct Foo {
template
explicit(!IsSafelyCastable::value) operator Foo();
};
template
template
Foo::operator Foo() {
return {};
}
int main() {
Foo a;
Foo b = a;
}
Clang 10 correctly evaluates the explicit condition to be true and blocks the
implicit cast. However, GCC 9.3.0 successfully compiles without any errors. I
believe this to be a GCC bug as subtle changes can make GCC produce the correct
error. For example, moving the definition of the function to be inline with the
declaration.
[Bug c++/95066] [C++ 20] Incorrect valid compilation with a conditional explicit
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95066
--- Comment #1 from Owen Smith ---
#include
template
class IsSafelyCastable : public std::false_type {};
template <>
class IsSafelyCastable : public std::true_type {};
template
struct Foo {
template
explicit(!IsSafelyCastable::value) operator Foo() { return {}; }
};
int main() {
Foo a;
Foo b = a;
}
Inlining the definition yields the correct error with GCC 9.3.0:
main.cpp: In function 'int main()':
main.cpp:17:18: error: conversion from 'Foo' to non-scalar type
'Foo' requested
17 | Foo b = a;
|
[Bug c++/95116] New: [C++ 20] Accepts invalid code with decltype dependent type
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95116
Bug ID: 95116
Summary: [C++ 20] Accepts invalid code with decltype dependent
type
Product: gcc
Version: 9.3.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: ojman101 at protonmail dot com
Target Milestone: ---
The code below is invalid. The keyword "typename" needs to be inserted before
the decltype expression as "bar" is a dependent type (dependent on template
type T).
template
struct Bar {
using bar_type = int;
};
template
struct Foo {
Bar bar;
using foo_type = decltype(bar)::bar_type;
};
int main() {
// Instantiate Foo template
Foo foo;
}
The code successfully compiles with GCC 9.3.0 when running the command "g++
-std=c++2a main.cpp". Note that the "-std=c++2a" must be passed. When passing
"-std=c++17", GCC successfully detects the error and prints:
main.cpp:10:22: error: need 'typename' before 'decltype
(((Foo*)(void)0)->Foo::bar)::bar_type' because 'decltype
(((Foo*)(void)0)->Foo::bar)' is a dependent scope
10 | using foo_type = decltype(bar)::bar_type;
| ^~~~
| typename
Running clang 10 with the command "clang++ -std=c++2a main.cpp" also
successfully detects the error and prints:
main.cpp:10:22: error: missing 'typename' prior to dependent type name
'decltype(bar)::bar_type'
using foo_type = decltype(bar)::bar_type;
^~~
typename
1 error generated.
[Bug c++/95116] [C++ 20] Accepts invalid code with decltype dependent type
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95116 --- Comment #2 from Owen Smith --- Ah ok thanks, I didn't know about P0634R3 :D.
