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11036 :: type mismatch when static uint32 is given to the slice operator

• dwhall256 (orginal) [2024-02-18T15:49:36+01:00] view original

  I have this code (playground) which I want to build compile-time consts. I've eliminated unrelated operations to hone in on my problem. The error is that toMask expects a Slice, but got an HSlice because the types of foo and baz differ; foo is becoming an int for a reason I do not understand.

  import std/bitops
  
  func mask(foo: static uint32, bar: static uint32): uint32 =
    const baz: uint32 = bar - 1
    const bim = toMask(foo .. baz)
    result = bim
  
  const m = mask(0, 1)
  Run

  My attempts to work around:

  1. Getting rid of baz's type declaration results in an unintuitive error bitops.nim(96, 14) Error: cannot instantiate: 'T'.
  2. Adding type: toMask[uint32] ... foo is still an int.

  I've read in docs that nim generally prefers signed int to unsigned types. I'm using uint32 here because I'm working in 32-bit microcontroller-land and want to avoid implicit sign extensions if I shift-right the value. If this is a C habit I need to purge, please help me understand.

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• dwhall256 (orginal) [2024-02-18T16:10:22+01:00] view original

  Oh, here it is. I looked at the declaration of toMask:

  func toMask*[T: SomeInteger](slice: Slice[int]): T {.inline, since: (1, 3).}
  Run

  Previously, I speed-read the SomeInteger and thought I was safe to use unsigned. But now I see the Slice is constrained to use signed values.

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• sls1005 (orginal) [2024-02-18T16:13:46+01:00] view original

  According to its prototype, the proc can only take Slice[int] (int-only), plus one additional generic type parameter (SomeInt). So it should be invoked as toMask[uint32](int(0) .. int(1) ). It seems that this generic parameter has to be given explicitly, similar to that of cast.

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