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10099 :: How can I know whether an untyped argument of a template can be stringified?

• 4n0n4me (orginal) [2023-04-14T15:25:40+02:00] view original

  I try to do this:

  template eval(body: untyped) =
    let res = body
    if isStringifyable(res):
      echo res
    else:
      discard
  Run

  I have known typeinfo in stdlib or concept may be helpful, but failed to use them successfully. I find no documentations for concepts. I wrote this with AI:

  type Stringifyable[T] = concept
    proc `$`(x: T): string
  Run

  But

  assert ((proc()=discard) is Stringifyable) == true
  Run

  while procedures actually can not be turned into strings.

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• 4n0n4me (orginal) [2023-04-14T15:42:07+02:00] view original

  Well, I find something in https://github.com/nim-lang/RFCs/issues/164 . I make mine like this:

  proc isStringifyableImpl[T](body: T): bool =
    type Helper = concept
      proc `$`(x: T): string
    result = body is Helper
  
  template isStringifyable(body: untyped): bool =
    let res = body
    isStringifyableImpl[typeof(res)](res)
  
  dump isStringifyable(1) # isStringifyable(1) = true
  dump isStringifyable(proc () = discard) # isStringifyable(proc () = (discard )) = false
  Run

  Seems working.

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• Araq (orginal) [2023-04-14T16:01:08+02:00] view original

  Try

  type Stringifyable = concept
    proc `$`(x: Self): string
  
  Run

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• xigoi (orginal) [2023-04-15T02:47:27+02:00] view original

  Or with old-style concepts:

  type Stringifyable = concept x
    $x is string
  Run

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