[Bug c++/50462] poor diagnostics for missing parenthesis in call to method
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=50462
--- Comment #7 from Jonathan Wakely ---
Oh, it's the overloaded function thjat makes the difference between saying
"invalid use of non-static member function" and trying to do overload
resolution with an .
Reduced example that actually reproduces the original problem:
struct ostream { };
void operator<<(ostream, int) { }
void operator<<(ostream, void*) { }
void operator<<(ostream, char*) { }
struct V
{
int size() { return 0; };
int size() const { return 0; };
};
void print(V v)
{ ostream() << v.size; }
Which prints this with current trunk:
50462.C: In function 'void print(V)':
50462.C:14:13: error: no match for 'operator<<' (operand types are 'ostream'
and '')
14 | { ostream() << v.size; }
| ~ ^~ ~~
| | |
| ostream
50462.C:3:6: note: candidate: 'void operator<<(ostream, int)'
3 | void operator<<(ostream, int) { }
| ^~~~
50462.C:3:26: note: no known conversion for argument 2 from '' to 'int'
3 | void operator<<(ostream, int) { }
| ^~~
50462.C:4:6: note: candidate: 'void operator<<(ostream, void*)'
4 | void operator<<(ostream, void*) { }
| ^~~~
50462.C:4:26: note: no known conversion for argument 2 from '' to 'void*'
4 | void operator<<(ostream, void*) { }
| ^
50462.C:5:6: note: candidate: 'void operator<<(ostream, char*)'
5 | void operator<<(ostream, char*) { }
| ^~~~
50462.C:5:26: note: no known conversion for argument 2 from '' to 'char*'
5 | void operator<<(ostream, char*) { }
| ^
I don't see why we should treat v.size any differently whether it's overloaded
or not. It's invalid either way, so we should fail similarly.
[Bug c++/50462] poor diagnostics for missing parenthesis in call to method
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=50462 --- Comment #6 from Jonathan Wakely --- (In reply to Jonathan Wakely from comment #5) > Since GCC 4.9 we don't perform overload resolution, so I think this is fixed: Huh, that's true for the reduced example in comment 4, but the original one from Chris still prints a wall of errors.
[Bug c++/50462] poor diagnostics for missing parenthesis in call to method
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=50462
--- Comment #5 from Jonathan Wakely ---
Since GCC 4.9 we don't perform overload resolution, so I think this is fixed:
50462.C: In function 'void print(V)':
50462.C:13:13: error: invalid use of non-static member function 'int V::size()'
13 | { ostream() << v.size; }
| ~~^
50462.C:9:13: note: declared here
9 | int size() { return 0; };
| ^~~~
[Bug c++/50462] poor diagnostics for missing parenthesis in call to method
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=50462
--- Comment #4 from Jonathan Wakely ---
I think the original example in this bug is the same as PR 77711 comment 2. It
can be reduced to:
struct ostream { };
void operator<<(ostream, int) { }
void operator<<(ostream, void*) { }
void operator<<(ostream, char*) { }
struct V
{
int size() { return 0; };
};
void print(V v)
{ ostream() << v.size; }
Now GCC's output fits on a single page:
50462.cc: In function 'void print(V)':
50462.cc:14:13: error: no match for 'operator<<' (operand types are 'ostream'
and '')
{ ostream() << v.size; }
~~^
50462.cc:3:6: note: candidate: void operator<<(ostream, int)
void operator<<(ostream, int) { }
^~~~
50462.cc:3:6: note: no known conversion for argument 2 from '' to 'int'
50462.cc:4:6: note: candidate: void operator<<(ostream, void*)
void operator<<(ostream, void*) { }
^~~~
50462.cc:4:6: note: no known conversion for argument 2 from '' to 'void*'
50462.cc:5:6: note: candidate: void operator<<(ostream, char*)
void operator<<(ostream, char*) { }
^~~~
50462.cc:5:6: note: no known conversion for argument 2 from '' to 'char*'
But Clang still does better, not bothering to perform overload resolution
hoping v.size will turn into something meaningful. Clang just says:
50462.cc:10:18: error: reference to non-static member function must be called;
did you mean to call it with no arguments?
{ std::cout << v.size; }
~~^~~~
()
50462.cc:5:6: note: possible target for call
int size() {};
^
50462.cc:6:6: note: possible target for call
int size() const {};
^
1 error generated.
So it doesn't bother telling us that every overload of operator<< is unusable
for a nonsense expression, which is much better.
EDG says:
"50462.cc", line 14: error: a pointer to a bound function may only be used to
call the function
{ ostream() << v.size; }
^
1 error detected in the compilation of "50462.cc".
This is a little cryptic and suggests there might be some non-standard
extension confusing matters.
[Bug c++/50462] poor diagnostics for missing parenthesis in call to method
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=50462
Jonathan Wakely changed:
What|Removed |Added
See Also||https://gcc.gnu.org/bugzill
||a/show_bug.cgi?id=77711
--- Comment #3 from Jonathan Wakely ---
See PR 77711 comment 1 where I said:
>It's irrelevant that we can't resolve which overload to use, once name lookup
>finds that 'foo' is a function then a.foo is not a valid expression under any
>circumstances.
The same applies here. The expression 'v.size' (when not followed by
parentheses) is not valid C++. Instead of trying to resolve which operator<<
can be used for a nonsense expression we should just give an error immediately
after parsing v.size, which is what Clang does:
50462.cc:10:18: error: reference to non-static member function must be called;
did you mean to call it with no arguments?
{ std::cout << v.size; }
~~^~~~
()
50462.cc:5:6: note: possible target for call
int size() {};
^
50462.cc:6:6: note: possible target for call
int size() const {};
^
1 error generated.
[Bug c++/50462] poor diagnostics for missing parenthesis in call to method
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=50462 Paolo Carlini changed: What|Removed |Added Status|UNCONFIRMED |NEW Last reconfirmed||2015-03-25 Ever confirmed|0 |1 --- Comment #2 from Paolo Carlini --- By the way, now clang does much better.
[Bug c++/50462] poor diagnostics for missing parenthesis in call to method
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50462
--- Comment #1 from Manuel López-Ibáñez 2011-09-20
13:59:47 UTC ---
Clang does only marginally better because of its selective typedef unwrapping
and avoiding printing back expressions, but then it goes and prints all
candidates:
/tmp/webcompile/_7569_0.cc:10:13: error: invalid operands to binary expression
('ostream' (aka 'basic_ostream') and '')
{ std::cout << v.size; }
~ ^ ~~
In file included from /tmp/webcompile/_7569_0.cc:1:
In file included from /usr/include/c++/4.3/iostream:44:
/usr/include/c++/4.3/ostream:111:7: note: candidate function not viable: no
overload of 'size' matching '__ostream_type &(*)(__ostream_type &)' for 1st
argument
operator<<(__ostream_type& (*__pf)(__ostream_type&))
^
/usr/include/c++/4.3/ostream:120:7: note: candidate function not viable: no
overload of 'size' matching '__ios_type &(*)(__ios_type &)' for 1st argument
operator<<(__ios_type& (*__pf)(__ios_type&))
^
/usr/include/c++/4.3/ostream:130:7: note: candidate function not viable: no
overload of 'size' matching 'std::ios_base &(*)(std::ios_base &)' for 1st
argument
operator<<(ios_base& (*__pf) (ios_base&))
^
/usr/include/c++/4.3/ostream:168:7: note: candidate function not viable: no
overload of 'size' matching 'long' for 1st argument
operator<<(long __n)
^
/usr/include/c++/4.3/ostream:172:7: note: candidate function not viable: no
overload of 'size' matching 'unsigned long' for 1st argument
operator<<(unsigned long __n)
^
/usr/include/c++/4.3/ostream:176:7: note: candidate function not viable: no
overload of 'size' matching 'bool' for 1st argument
operator<<(bool __n)
^
/usr/include/c++/4.3/ostream:180:7: note: candidate function not viable: no
overload of 'size' matching 'short' for 1st argument
operator<<(short __n);
^
/usr/include/c++/4.3/ostream:183:7: note: candidate function not viable: no
overload of 'size' matching 'unsigned short' for 1st argument
operator<<(unsigned short __n)
^
/usr/include/c++/4.3/ostream:191:7: note: candidate function not viable: no
overload of 'size' matching 'int' for 1st argument
operator<<(int __n);
^
/usr/include/c++/4.3/ostream:194:7: note: candidate function not viable: no
overload of 'size' matching 'unsigned int' for 1st argument
operator<<(unsigned int __n)
^
/usr/include/c++/4.3/ostream:203:7: note: candidate function not viable: no
overload of 'size' matching 'long long' for 1st argument
operator<<(long long __n)
^
/usr/include/c++/4.3/ostream:207:7: note: candidate function not viable: no
overload of 'size' matching 'unsigned long long' for 1st argument
operator<<(unsigned long long __n)
^
/usr/include/c++/4.3/ostream:212:7: note: candidate function not viable: no
overload of 'size' matching 'double' for 1st argument
operator<<(double __f)
^
/usr/include/c++/4.3/ostream:216:7: note: candidate function not viable: no
overload of 'size' matching 'float' for 1st argument
operator<<(float __f)
^
/usr/include/c++/4.3/ostream:224:7: note: candidate function not viable: no
overload of 'size' matching 'long double' for 1st argument
operator<<(long double __f)
^
/usr/include/c++/4.3/ostream:228:7: note: candidate function not viable: no
overload of 'size' matching 'const void *' for 1st argument
operator<<(const void* __p)
^
/usr/include/c++/4.3/ostream:253:7: note: candidate function not viable: no
overload of 'size' matching '__streambuf_type *' (aka 'basic_streambuf > *') for 1st argument
operator<<(__streambuf_type* __sb);
^
/usr/include/c++/4.3/ostream:449:5: note: candidate function [with _CharT =
char, _Traits = std::char_traits] not viable: no overload of 'size'
matching 'char' for 2nd argument
operator<<(basic_ostream<_CharT, _Traits>& __out, _CharT __c)
^
/usr/include/c++/4.3/ostream:454:5: note: candidate function [with _CharT =
char, _Traits = std::char_traits] not viable: no overload of 'size'
matching 'char' for 2nd argument
operator<<(basic_ostream<_CharT, _Traits>& __out, char __c)
^
/usr/include/c++/4.3/ostream:460:5: note: candidate function [with _Traits =
std::char_traits] not viable: no overload of 'size' matching 'char' for
2nd argument
operator<<(basic_ostream& __out, char __c)
^
/usr/include/c++/4.3/ostream:466:5: note: candidate function [with _Traits =
std::char_traits] not viable: no overload of 'size' matching 'signed
char' for 2nd argument
operator<<(basic_ostream& __out, signed char __c)
^
/usr/include/c++/4.3/ostream:471:5: note: candidate function [with _Traits =
std::char_traits] not viable: no overload of 'size' matching 'unsigned
char' for 2nd argument
operator<<(basic_ostream& __out, unsigned char __c)
^
/usr/include/c++/4.3/ostream:491:5: note: candidate function [with _CharT =
char, _Traits = std::char_traits] not viable: no overload of 'size'
