FnOnce<Args>
call_once(self, Args) -> Output
FnMut<Args>
call_mut(&mut self, Args) -> Output
Fn<Args>
call(&self, Args) -> Output
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yeah… really screams out for some sort of polymorphism over closure usage… or something like that
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tbh this is fine? because they're all supertraits and because lifetimes, ownership, and mutability matters, you can and indeed must specify the strictness of your trait bound, which lets you accept either all closures (FnOnce) or ones that are safe to call repeatedly (Fn).
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Yeah I agree it works fine in Rust, yeah… but I think I'd want closures to be able to support other substructural properties beyond what Rust supports? And then you start getting more and more traits? But yeah I haven't thought it through carefully yet 😅
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Thinking about stuff like information flow, stage, and usage counts - say if your language supported being able to specify a range of times a closure can be used.
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Mmm, fairly limited gain from going from
FnOnce for 0 | 1 calls
FnMut for 0..X calls
Fn for 0.. calls
to
Fn [X] for 0..X calls
because while the X is hidden in FnMut you can wrap Option and return Some until None.
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I'd say you'd want something more like:
Fn [0..1] for FnOnce
Fn [0..] for Fn
Fn [0.., Unique] for FnMut (not sure about this one)
This would also give you other stuff, like:
Fn [1] for a closure that *must* be used
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But yeah, there are lots of unknowns, but I'd encourage you to look at some of the Granule demos that show some of the automation and error checking you get from the more precise types
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Found an old talk that might be of interest! Sorry if I sound like I'm shilling this stuff pretty hard – there is a bunch of stuff that would need to be done to make this work for systems programming, but I think it seems promising!
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Explain to me how it would help me make a more-correct compiler to assembly or a better API for SIMD or floating point.
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I'm not sure about the specifics of SIMD, but I think there are levels of SIMD support for different processors? You could that support as part of the API, and ensure that certain properties have been checked for before calling certain ops.
I already have adequate solutions for that, actually, and a compiler is unlikely to place the check patterns correctly because that depends on out-of-band information, so it is fine to insist the programmer do so.
You see, in today's world you need to account for code mobility.
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That, or you need to simply make it UB to move from machine with higher feature levels to a lower feature level.
But it would be totally unacceptable to make the check before every call in to a SIMD function. It's enough to make the choice based on entering the right scope.
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