https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69731
Bug ID: 69731
Summary: Inconsistent SFINAE in interaction with variable
templates
Product: gcc
Version: 6.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: lucdanton at free dot fr
Target Milestone: ---
Created attachment 37641
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=37641&action=edit
Minimal testcase
It appears that GCC behaves differently depending on how SFINAE is performed
(e.g. how a trait is written), and how a trait is used(!) at the constraint
site (using regular enable_if_t techniques). In one particular case one of the
techniques loops until the instantiation limit depth is reached, but only if
the
short form is used on the site. Regardless of what /should/ happen (which I
have no idea about), I believe GCC should consistently either loop or
terminate.
For what it's worth Clang accepts all cases for both forms.
I am using 6.0.0 20160208, the testcase is compiled with alternatively:
g++-trunk -std=c++1z -DSHORT testcase.cpp
g++-trunk -std=c++1z testcase.cpp
The first command results in constraints that use trait_v<X, Y> variable
templates
and succeeds. The second command results in constraints that use the
trait<X, Y>::value static members and hits the limit.
