Commit 22a5896e authored by Marshall Cline's avatar Marshall Cline Committed by Facebook Github Bot

remove lvalue-qual Future::semi()

Summary:
This is part of "the great r-valuification of folly::Future":
* This is something we should do for safety in general.
* Several of folly::Future's methods are lvalue-qualified even though they act as though they are rvalue-qualified, that is, they provide a postcondition that says, in effect, callers should act as though the method invalidated its `this` object (regardless of whether that invalidation was actual or logical).
* This violates the C++ principle to "Express ideas directly in code" (see Core Guidelines), and generally makes it more confusing for callers as well as hiding the actual semantics from tools (linters, compilers, etc.).
* This dichotomy and confusion has manifested itself by some failures around D7840699 since lvalue-qualification hides that operation's move-out semantics - leads to some use of future operations that are really not correct, but are not obviously incorrect.
* The goal of rvalueification is to make sure methods that are logically rvalue-qualified are actually rvalue-qualified, which forces callsites to acknowledge that rvalueification, e.g., `std::move(f).semi()` instead of `f.semi()`. This syntactic change in the callsites forces callers to acknowledge the method's rvalue semantics.

Reviewed By: LeeHowes

Differential Revision: D9442704

fbshipit-source-id: 50b1912e33ac23d1a693682fbcd55cd637cdb149
parent eab02f06
...@@ -1867,10 +1867,6 @@ class Future : private futures::detail::FutureBase<T> { ...@@ -1867,10 +1867,6 @@ class Future : private futures::detail::FutureBase<T> {
return SemiFuture<T>{std::move(*this)}; return SemiFuture<T>{std::move(*this)};
} }
SemiFuture<T> semi() & {
return std::move(*this).semi();
}
protected: protected:
friend class Promise<T>; friend class Promise<T>;
template <class> template <class>
......
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