Why Does GCC Fail to Compile Explicit Specializations in Non-Namespace Scope?

Explicit Specializations in Non-Namespace Scope: GCC Compilation Issue

Despite complying with the C standard, which explicitly permits explicit specializations in any scope where the primary template can be defined, the provided code exhibits compilation errors in GCC but not in Clang. This discrepancy raises the question of whether this is a bug in GCC and how to locate it in its bug tracker.

According to [temp.expl.spec], paragraph 2, "An explicit specialization may be declared in any scope in which the corresponding primary template may be defined." However, GCC HEAD 8.0.1 with -std=c 2a produces an error message indicating that the explicit specialization is not allowed in a non-namespace scope.

This deviation from the standard suggests a potential bug in GCC. To locate this issue in the bug tracker, one can search for "explicit specialization" or "scope" in the GCC bug database. Alternatively, the issue can be reported directly using the bug reporting system.

In this case, the issue has been reported as Bug 85282, which acknowledges the problem and its inconsistency with the CWG 727 amendment. The amendment revised the standard to allow explicit specializations in any scope where the primary template can be defined.

The implication of this bug is that GCC users may encounter compilation issues when attempting to declare explicit specializations outside of namespace scope, despite the C standard permitting such declarations. To mitigate this issue, users can either target non-GCC compilers or encapsulate the explicit specialization within a namespace, which is currently the only scope compatible with GCC's interpretation of the standard.

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