Commit fdfdc324 authored by Marshall Cline's avatar Marshall Cline Committed by Facebook Github Bot

remove lvalue-qual Future::onError(...)

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).onError(...)` instead of `f.onError(...)`. This syntactic change in the callsites forces callers to acknowledge the method's rvalue semantics.

Reviewed By: yfeldblum

Differential Revision: D9441402

fbshipit-source-id: 1c39ca7b33bb406d2fd3a995f487693a2d013747
parent 3411b8c6
......@@ -1476,11 +1476,6 @@ class Future : private futures::detail::FutureBase<T> {
Future<T>>::type
onError(F&& func) &&;
template <class F>
auto onError(F&& func) & {
return std::move(*this).onError(std::forward<F>(func));
}
/// func is like std::function<void()> and is executed unconditionally, and
/// the value/exception is passed through to the resulting Future.
/// func shouldn't throw, but if it does it will be captured and propagated,
......
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