This footgun is the reason I'm so enthusiastic about the Rust `become` keyword.

This proposal would give Rust a specific keyword which says that you intend TCO and so two things happen: 1. The compiler goes to more length to deliver TCO even where it wouldn't "just work" and 2. If it cannot deliver TCO your code doesn't compile, because you asked for TCO.

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chriswarbo an hour ago | parent | next [-]

Sounds similar to @tailrec in Scala

I personally use the phrase "tail call elimination" when it's a requirement that can be relied on; and "tail call optimisation" when it might be implementation-dependent, context-dependent, limited (e.g. to immediate self-calls), etc.

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StilesCrisis 2 hours ago | parent | prev [-]

Sounds like clang::must_tail?

	▲	tialaramex an hour ago \| parent [-]
		I am not a Clang expert, but first, obviously that's a C++ attribute and so while Clang can decide what it means in Clang in the programming language itself it has no semantic weight because the ISO document says attributes are always ignorable. Secondly however in these languages you often won't naively get TCO because you have at least one local variable which C++ would say has a "non-trivial destructor" or Rust would say "implements Drop". These both mean that naively the "tail call" wasn't actually the last thing to happen, the destructor / Drop::drop happen at the end of the function, after the tail call. The proposed become keyword tries to core::mem::drop any such variables, if it succeeds now that tail call is last and we can do TCO, if it fails [e.g. because the variables it wants to drop are needed for the tail call] we can diagnose the problem. I believe the Clang attribute doesn't have this behaviour.