function rm(node) {
for (const child of ls(node))
rm(child);
unlink(node);
}
[1] https://github.com/rust-lang/rust/issues/112788
[2] https://github.com/rust-lang/rust/issues/153827
By-default guaranteed tail calls really isn't rust's style, because it means subtle changes (introducing a destructor, re-ordering code, etc) can change semantics without you realizing it. If you want to guarantee that a call can't allocate a new stack frame you should have to say it.
But I can understand the preference for an explicit opt-in, to make clear that it is enforced and not assumed.
I'd argue that it's explicit - that's what a function call does and you don't have implicit function calls in rust.
> Seems the latter is a kind of compiler-level optimization, of which there are already many (I think) that change the semantics internally but guarantee the outward behavior stays the same.
What you're asking for here already exists. Tail calls might be optimized into not allocating extra stack frames, the rust compiler just doesn't guarantee that it will perform that optimization (and almost certainly won't when code is compiled without optimizations... for instance).
What people want is the semantic guarantee that the stack frame won't be allocated. Not just a compiler that often performs the optimization. Otherwise you can't be sure that your code will keep working with new compiler flags/versions/architectures/... You could say "whenever the code is the right shape we'll guarantee the optimization" (C++ famously did this for things like copy elision)... but now the shape of code comes with non-obvious semantic guarantees and that's not rust's style. Hence the proposal for a keyword instead.
No, it won't change semantics - if you say @musttail or similar, it will simply fail to compile if you, say, introduce a destructor - the semantics will not subtly change.
The whole idea of "let's change semantics to make it easier" is dumb.
If you want guaranteed tail calls, change your code until it works.
For recursion only kotlin.
(For most of these only with syntax specifying it)