https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91803
Bug ID: 91803
Summary: statement-expressions are not allowed in template
arguments
Product: gcc
Version: 10.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: bernd.edlinger at hotmail dot de
Target Milestone: ---
I wanted to use something like __typeof(ORIGINAL_REGNO(rtl)) in a template
argument, but it does not work, I wonder if that is a bug.
$ cat test.cc
template <class X>
X identity(X x)
{ return x; }
#define IDENTITY(X) __extension__ \
({ __typeof(X) const x = (X); x; })
int
main()
{
/* error: statement-expressions are not allowed
outside functions nor in template-argument lists */
if (identity<__typeof(IDENTITY(0))>(1) != 1);
__builtin_abort();
/* but this works! */
if (identity<__typeof(identity<__typeof(0)>(0))>(1) != 1)
__builtin_abort();
}
$ g++ test.cc
test.cc: In function 'int main()':
test.cc:6:1: error: statement-expressions are not allowed outside functions nor
in template-argument lists
6 | ({ __typeof(X) const x = (X); x; })
| ^
test.cc:13:25: note: in expansion of macro 'IDENTITY'
13 | if (identity<__typeof(IDENTITY(0))>(1) != 1);
| ^~~~~~~~
test.cc:13:40: error: no matching function for call to 'identity<<expression
error> >(int)'
13 | if (identity<__typeof(IDENTITY(0))>(1) != 1);
| ^
test.cc:2:3: note: candidate: 'template<class X> X identity(X)'
2 | X identity(X x)
| ^~~~~~~~
test.cc:2:3: note: template argument deduction/substitution failed:
test.cc:13:40: error: template argument 1 is invalid
13 | if (identity<__typeof(IDENTITY(0))>(1) != 1);
| ^
