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581 :: Testing for type class membership

• mason_mcgill (orginal) [2014-10-10T07:48:15+02:00] view original

  Hi,

  I'm hoping someone familiar with the compiler/language specification could clarify something for me. The manual states that "user defined type classes will be instantiated exactly once for each tested type and any static code included within them will also be executed once."

  However, when I run the following code, it (quite reasonably) seems to test a single type for type class membership twice:

  type Printable = generic x
    print x
  
  proc check() = echo Int is Printable
  proc print(x: Int) = echo "Printing an integer: ", x
  proc checkAgain() = echo Int is Printable
  
  check() # prints "false"
  checkAgain() # prints "true"
  Run

  So, in general, when exactly are generic blocks evaluated (or is this an implementation detail)?

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• Araq (orginal) [2014-10-10T09:59:10+02:00] view original

  Testing is not instantiation. But you're right, we need to clarify these things.

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• mason_mcgill (orginal) [2014-10-10T18:06:24+02:00] view original

  Out of curiousity--what exactly does "instatiation" mean for a type class in Nim? Or are you referring to the instantiation of a proc parameterized by an instance of a type class? Or should I just eagerly anticipate the next release of the manual : )

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