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6979 :: Docs: Remove gensym from arguments for procs defined in templates?

• benjamindlee (orginal) [2020-10-23T17:16:47+02:00] view original

  I'm working on a little library with a bunch of distinct string types. Using the advice in the manual, I made a template to define the string operations I need:

  template defineStrOprs(typ: typedesc) =
    proc `$`*(x: typ): string {.borrow.}
    proc `&`*(x, y: typ): typ = typ($x & $y)
    proc `&=`*(x: var typ, y: typ) {.borrow.}
    proc `[]`*[T, U](x: typ; h: HSlice[T, U]): typ = typ(($x)[h])
    ...
  Run

  When I run nim doc, I get "gensym'd" arguments:

  proc `$`(x`gensym12636101: Dna): string {...}
  Run

  I'm concerned downstream users of this library (likely to be novices) will be put off. Is there a way to remove it from the docs?

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• timothee (orginal) [2020-10-23T18:19:07+02:00] view original

  I'm still not convinced that gensym parameters are a good idea, see full discussion in https://github.com/nim-lang/Nim/issues/12020

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• benjamindlee (orginal) [2020-10-23T18:49:42+02:00] view original

  Thanks for the link. I looked at the pragmas mentioned in response to your comment and am still a bit lost. I was able to declare the template as dirty (which I think is safe) and that worked but doesn't feel robust.

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• shirleyquirk (orginal) [2020-10-23T19:23:02+02:00] view original

  read over https://nim-lang.org/docs/manual.html#templates-hygiene-in-templates for a better explanation of {.dirty.} {.gensym.} and {.inject.}

  {.dirty.} is probably the best solution for your case, otherwise you have to annotate everything with {.inject.}

  template defineStrOprs(typ: typedesc) =
    proc `$`*(x:{.inject.} typ): string {.borrow.}
    proc `&`*(x{.inject.}, y{.inject.}: typ): typ = typ($x & $y)
    proc `&=`*(x{.inject.}: var typ, y{.inject.}: typ) {.borrow.}
    proc `[]`*[T, U](x{.inject.}: typ; h{.inject.}: HSlice[T, U]): typ = typ(($x)[h])
  Run

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• benjamindlee (orginal) [2020-10-23T22:31:18+02:00] view original

  Thanks shirleyquirk. That's what I ended up doing.

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