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clang allows forming pointer to function with cv-qualifier-seq or ref-qualifier #20116

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llvmbot opened this issue May 14, 2014 · 2 comments
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bugzilla Issues migrated from bugzilla c++11

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@llvmbot
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llvmbot commented May 14, 2014

Bugzilla Link 19742
Version trunk
OS Linux
Reporter LLVM Bugzilla Contributor
CC @DougGregor,@zygoloid

Extended Description

When compiling the following code using C++11 options:

-Wall -Wextra -std=c++11 -pedantic

or using C++1y options:

-Wall -Wextra -std=c++1y -pedantic

it is accepted by clang 3.5 trunk 208701 or 3.4 final:

//---------------------
template
struct add_ptr
{
using type = T*;
};

int main() {
using FC = void () const;
using PFC = add_ptr::type;
using FLR = void () &;
using PFLR = add_ptr::type;
using FRR = void () &&;
using PFRR = add_ptr::type;
}
//---------------------

After resolution of CWG 1417,

http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_defects.html#1417

the formation of a pointer to function types with cv-qualifier or ref-qualifier (even in template context) is not supported. In non-template context, clang already rejects such an attempt.

The code had been compiled using the online-compiler

http://melpon.org/wandbox/

therefore the provided information about OS and hardware are guesses on my side.

@zygoloid
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zygoloid mannequin commented May 15, 2014

Fixed in r208825, but I'm leaving this open because we're not done here yet. We still incorrectly accept these:

template struct S {
void f(T);
};
S<void () const> s1;
S<void () &> s2;

... because we don't properly validate the pointer type we build when performing function-to-pointer decay.

@llvmbot
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llvmbot commented Feb 19, 2016

Fixed in r208825, but I'm leaving this open because we're not done here yet.
We still incorrectly accept these:

template struct S {
void f(T);
};
S<void () const> s1;
S<void () &> s2;

... because we don't properly validate the pointer type we build when
performing function-to-pointer decay.

Good afternoon,

so, in the context of this question I would like to clarify, that this rule (8.3.1/4):
"Forming a reference to function type is ill-formed if the function type has cv-qualifiers or a ref-qualifier"

applicable for this code:

#include

template
void (* test()) (F);

template
char (& probe( void(*) ( X * ) ) )[1];

template
char (& probe( void(*) ( X ) ) )[2];

int main()
{
std::cout << sizeof(probe(test<void() const>()));
}
in context of C++14 standard (for versions 3.4 and earlier this code prints "1", 3.5 and higher prints "2")?

And what about C++03 (in which there is no explicit limitation)? Behaviour whould same, or not?

@llvmbot llvmbot transferred this issue from llvm/llvm-bugzilla-archive Dec 9, 2021
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