[PATCH] PR libstdc++/87855 fix optional for types with non-trivial copy/move

[Jonathan Wakely]

On 08/01/19 23:00 +0000, Jonathan Wakely wrote:
>When the contained value is not trivially copy (or move) constructible
>the union's copy (or move) constructor will be deleted, and so the
>_Optional_payload delegating constructors are invalid. G++ fails to
>diagnose this because it incorrectly performs copy elision in the
>delegating constructors. Clang does diagnose it (llvm.org/PR40245).
>
>The solution is to avoid performing any copy (or move) when the
>contained value's copy (or move) constructor isn't trivial. Instead the
>contained value can be constructed by calling _M_construct. This is OK,
>because the relevant constructor doesn't need to be constexpr when the
>contained value isn't trivially copy (or move) constructible.
>
>Additionally, this patch removes a lot of code duplication in the
>_Optional_payload partial specializations and the _Optional_base partial
>specialization, by hoisting it into common base classes.

This follow-up patch removes a little more code duplication from those
partial specializations.

Tested x86_64-linux. Ville already ack'd this, so I'm committing it to trunk.


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