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2747 :: type mismatch assigning function pointer? gcsafeness confusion?

• luked2 (orginal) [2017-01-23T17:27:07+01:00] view original

  Hi!

  What am I doing wrong here:

  
  type
    FooProc = proc(x: int)
    
    Callbacks = tuple [
      cb: FooProc
    ]
  
  proc foo(x: int) : void = echo "foo: " & $x
  
  let f:FooProc = foo
  
  let c0: Callbacks = (cb: f)    # works fine
  let c1: Callbacks = (cb: foo)  # type mismatch!
  
  c0.cb(42)
  c1.cb(42)
  Run

  The assignment to c1 complains, saying:

  : type mismatch: got (tuple[cb: proc (x: int){.gcsafe, locks: 0.}]) but expected 'Callbacks = tuple[cb: FooProc]'
  Run

  But surely f and foo are the same? Shouldn't that assignment either always fail, or always be OK? What am I missing?

  Thanks!

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• Araq (orginal) [2017-01-24T12:25:01+01:00] view original

  They are not the same, the proc type is .closure the proc is .nimcall. There is an automatic conversion from nimcall to closure but not in tuple constructors (for better or worse).

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• bpr (orginal) [2017-01-24T17:19:16+01:00] view original

  There is an automatic conversion from nimcall to closure but not in tuple constructors (for better or worse).

  What are the precise conditions under which one should choose a tuple over an object? I'd use them for points in n-space for small n, and other tasks where I wrap up a very small number of builtin types and I expect a lot of them, but not much else. I almost always use objects, because tuples often surprise me.

  In this case, using an object works as @luked2 expected.

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