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455 :: Can a proc modify its behaviour at runtime?

• gradha (orginal) [2014-05-24T18:04:57+02:00] view original

  Let's say that I have a proc which does something singleton-like, it initializes internal structures and later only executes a different branch of code which depends on those structures. The layout would be something like this:

  
  proc foo() =
    if global_not_initialized:
      initialize_stuff()
    else:
      use_initialized_stuff()
  Run

  Can a proc rewrite itself at runtime? The purpose would be for initialize_stuff() to rewrite the behaviour of foo() to actually embed the contents from use_initialized_stuff() directly, avoiding the boolean check and internal function call. Callers would be oblivious to this internal trickery.

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• Jehan (orginal) [2014-05-24T19:04:47+02:00] view original

  Simply make it a procedure variable. E.g.:

  
  var foo: proc()
  
  proc use_initialized_stuff() =
    echo "use"
  
  proc initialize_stuff() =
    echo "init"
    foo = use_initialized_stuff
  
  foo = initialize_stuff
  
  foo()
  foo()
  Run

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• gradha (orginal) [2014-05-24T21:37:20+02:00] view original

  Doesn't the use of a variable defeat the objective of avoiding branching inside the proc?

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• Jehan (orginal) [2014-05-24T21:51:21+02:00] view original

  If that's your concern, I wouldn't worry about it. The branch prediction logic of modern CPUs will essentially wipe out any overhead from the check, given that the code will always take the same branch after the first time.

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