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2190 :: 'var' placement inside proc definitions versus outside

• Zeno_X (orginal) [2016-04-08T22:47:03+02:00] view original

  Related to an issue (https://github.com/nim-lang/Nim/issues/4067) I opened about an unhelpful error message, I'd like to ask here why 'var' is before a variable but after a proc parameter, from a grammar/design view?

  var p: int versus proc doSomethingToP(p: var int)...

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• leledumbo (orginal) [2016-04-09T06:06:20+02:00] view original

  Clearer semantics from syntax?

  var p: int
  Run

  declares a variable named p of type int. While p in:

  proc doSomethingToP(p: var int)
  Run

  declares a parameter named p of type modifiable int. It's like tying parameter passing as part of the parameter type. AFAICS, there should be no noticable difference in grammar/design/parsing view of such a syntax.

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• Stefan_Salewski (orginal) [2016-04-09T08:46:08+02:00] view original

  In Modula 2 and OBERON we had

  proc doSomethingToP(var p: int)
  Run

  so var in front of the identifier tells us that it can be modified. I was always happy with that notation -- in Nim I did it the old way a few times. but now I generally can remember it. Maybe the Nim notation is indead more clear because the name of the variable resides at the left, not in the middle of var keyword and type.

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• Araq (orginal) [2016-04-09T17:02:42+02:00] view original

  var is actually close to ref and ptr, for example type VInt = var int is also supported (though nobody uses it). var is clearly part of the type, it's not a parameter passing mode. Another inspiration for this syntax was Ada (in Ada it's x: in out T).

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