在 2022/12/2 08:17, leon zadorin via Gcc-help 写道:
Thanks Jonathan for clarifying, as always - very precise and helpful. I'll close the issue on the clang side also.
No, you do not _instantiate_ `J<X>`. The behavior would have been undefined if you did. `::std::shared_ptr<J<X>> p;` is fine on itself, because `J<X>` is not instantiated. On the other hand, `::std::shared_ptr<J<X>> p(static_cast<J<X>*>(nullptr));` is undefined, as it instantiates a delete expression.
In addition to that, [temp.point]/1 specifies that the point of instantiation of members of a class template _follows the end of_ namespace scope of the most enclosing specialization. This allows use before definition, which is not permitted for non-template classes:
std::shared_ptr<struct foo> ptr(
(struct foo*) nullptr); // instantiates `delete (struct foo*) ___`
struct foo { }; // the line above would have undefined behavior without this
So, either way, your code is not undefined.
--
Best regards,
LIU Hao
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