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.
Conversation
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.
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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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I'm not talking about checking on every call, I'm talking about ensuring that you a calling in a context where the check has previously been made 😅
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'cache invalidation': need to account for the case that the running app and that context you mention just teleported to a vm host with a different (gen) cpu
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Ohhh interesting! That does sound painful 😖