http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54738
Bug #: 54738
Summary: [C++11][SFINAE] Hard errors for pointer-to-member
function expressions
Classification: Unclassified
Product: gcc
Version: 4.8.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: daniel.krueg...@googlemail.com
During my attempts to implement sfinae-friendly result_of I found the following
problems using gcc 4.8.0 20120923 (experimental) with compile-flags
-Wall -pedantic -std=c++0x
with pointer-to-member function expressions.
First there are problems if we have an incompatible number of function call
arguments:
//---
template<class T>
T&& declval();
template<class F, class T1, class... Ts>
decltype(((*declval<T1>()).*declval<F>())(declval<Ts>()...))
test1(int);
template<class...>
void test1(...);
template<class F, class T1, class... Ts>
decltype((declval<T1>().*declval<F>())(declval<Ts>()...))
test2(int);
template<class...>
void test2(...);
struct S {};
typedef void (S::*Func)(int) const;
typedef decltype(test1<Func, S*>(0)) type1a; // #22
typedef decltype(test1<Func, S*&>(0)) type1b;
typedef decltype(test1<Func, S*, int, int>(0)) type1c;
typedef decltype(test1<Func, S*&, int, int>(0)) type1d;
typedef decltype(test2<Func, S>(0)) type2a; // #27
typedef decltype(test2<Func, S&>(0)) type2b;
typedef decltype(test2<Func, S, int, int>(0)) type2c;
typedef decltype(test2<Func, S&, int, int>(0)) type2d;
//---
The error messages are:
<quote>
22| required from here|
6|error: too few arguments to function|
22| required from here|
6|error: too few arguments to function|
23| required from here|
6|error: too few arguments to function|
23| required from here|
6|error: too few arguments to function|
24| required from here|
6|error: too many arguments to function|
25| required from here|
6|error: too many arguments to function|
27| required from here|
13|error: too few arguments to function|
27| required from here|
13|error: too few arguments to function|
28| required from here|
13|error: too few arguments to function|
28| required from here|
13|error: too few arguments to function|
29| required from here|
13|error: too many arguments to function|
30| required from here|
13|error: too many arguments to function|
</quote>
Further there are also problems with corresponding function call expressions
where the arguments won't convert:
//---
template<class T>
T&& declval();
template<class F, class T1, class... Ts>
decltype(((*declval<T1>()).*declval<F>())(declval<Ts>()...))
test1(int);
template<class...>
void test1(...);
template<class F, class T1, class... Ts>
decltype((declval<T1>().*declval<F>())(declval<Ts>()...))
test2(int);
template<class...>
void test2(...);
struct S {};
typedef void (S::*Func)(int) const;
typedef decltype(test1<Func, S*, S>(0)) type3a; // #22
typedef decltype(test1<Func, S*&, S>(0)) type3b;
typedef decltype(test2<Func, S, S>(0)) type4a; // #25
typedef decltype(test2<Func, S&, S>(0)) type4b;
//---
The error messages are:
<quote>
22| required from here|
6|error: cannot convert 'S' to 'int' in argument passing|
22| required from here|
6|error: cannot convert 'S' to 'int' in argument passing|
23| required from here|
6|error: cannot convert 'S' to 'int' in argument passing|
23| required from here|
6|error: cannot convert 'S' to 'int' in argument passing|
25| required from here|
13|error: cannot convert 'S' to 'int' in argument passing|
25| required from here|
13|error: cannot convert 'S' to 'int' in argument passing|
26| required from here|
13|error: cannot convert 'S' to 'int' in argument passing|
26| required from here|
13|error: cannot convert 'S' to 'int' in argument passing|
</quote>
Further cv-violations aren't sfinaed away:
//---
template<class T>
T&& declval();
template<class F, class T1, class... Ts>
decltype(((*declval<T1>()).*declval<F>())(declval<Ts>()...))
test1(int);
template<class...>
void test1(...);
template<class F, class T1, class... Ts>
decltype((declval<T1>().*declval<F>())(declval<Ts>()...))
test2(int);
template<class...>
void test2(...);
struct S {};
typedef void (S::*Func2)(int);
typedef decltype(test1<Func2, const S*, int>(0)) type5a; // #22
typedef decltype(test1<Func2, const S*&, int>(0)) type5b;
typedef decltype(test2<Func2, const S, int>(0)) type6a; // #25
typedef decltype(test2<Func2, const S&, int>(0)) type6b;
//---
The error messages are:
<quote>
22| required from here|
6|error: invalid conversion from 'const S*' to 'S*' [-fpermissive]|
23| required from here|
6|error: invalid conversion from 'const S*' to 'S*' [-fpermissive]|
25| required from here|
13|error: invalid conversion from 'const S*' to 'S*' [-fpermissive]|
26| required from here|
13|error: invalid conversion from 'const S*' to 'S*' [-fpermissive]|
</quote>
These code examples should all be accepted.
