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8945 :: Knowledge on the failure in overloaded operator of two operands infix ?

• mardiyah (orginal) [2022-02-24T13:36:07+01:00] view original

  How to have Nim overloaded operator i.e. two operands infix operator ? e.g

  ` s .= function()` to mean s = s.function()

  on:

   std/nre
  
  template `.=`( a :string; b :proc( m :untyped, n:untyped) ) =
    var a :string = a.b
  
  var
    s="hello world !"
  
  s .= replace(re"\w+", "masked")
  
  echo s
  Run

  fails with

  ..................Traceback from system (most recent call last)
  SIGSEGV: Illegal storage access. (Attempt to read from nil?)
  
  
  ------------------
  (program exited with code: 1)
  Run

  And other errors for other tried tiny variations

  Sincerely, help out please

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• PMunch (orginal) [2022-02-24T13:58:41+01:00] view original

  The fact that it crashes seems to be a compiler bug. But you're not going to be able to do it this way for a couple of reasons:

  1. .= is a dot-operator which has a special meaning in Nim
  2. That template won't match what you're doing, replace(re"\w+", "masked") isn't a proc with two arguments, it's a call to a procedure.
  3. Templates can't perform that kind of transformation

  That being said you can make it work with a macro and a slightly different operator:

  import std/nre, macros, sequtils
  
  macro `:=`(a: var string; b: untyped): untyped =
    var call = b
    call.insert(1, a)
    result = quote do:
      `a` = `call`
    echo result.repr
  
  var s = "hello world !"
  
  s := replace(re"\w+", "masked")
  
  echo s
  Run

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• sls1005 (orginal) [2022-02-24T14:59:41+01:00] view original

  Dot operators are available via {.experimental.}.

  {.experimental: "dotOperators".}
  
  macro `.=`(s: string, call: untyped): untyped =
    discard
  Run

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• PMunch (orginal) [2022-02-24T15:59:24+01:00] view original

  Yes, but the .= operator has a different meaning than just a normal operator. When you enable that experimental it will match https://nim-lang.org/docs/manual_experimental.html#special-operators-operator-nimdoteq.

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• sls1005 (orginal) [2022-02-24T16:22:45+01:00] view original

  But it's `.=`(a, b, c). Is `.=`(a, b) also special?

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• Araq (orginal) [2022-02-24T17:52:58+01:00] view original

  Use std/with.

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