https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98660
Bug ID: 98660
Summary: -Wold-style-cast should not warn on casts that look
like (decltype(x))(x)
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: gasper.azman at gmail dot com
Target Milestone: ---
Dear GCC wizards,
Recently, the use of std::forward has been idiomatically replaced by the
following:
```
template <typename T>
void george(T&& x) {
john((T&&)x); // means std::forward<T>(x)
}
```
Casting an `x` to `decltype(x)` is far shorter and faster to compile (which
matters since it's done in unevaluated contexts A LOT). For an example, observe
the usage in libunifex, the in-progress research implementation of the
executors proposal:
https://github.com/facebookexperimental/libunifex/blob/master/include/unifex/tag_invoke.hpp
Unfortunately, the only real way to combine this fairly important exception to
the general rules of "no c-style casts" is to disable -Wold-style-cast.
It would be a great benefit if I could leave that warning enabled, and sleep
soundly in the knowledge I didn't mistype the forwarding expression if gcc
checked for me that the type I'm casting to is, in fact, `decltype(x)`, and
complain otherwise.
Please consider this refinement for a future release of GCC.
Thank you.
