Re: User-reserved element in byte code vectors

[Lars Brinkhoff <lars@nocrew.org>]

Stefan Monnier <monnier@iro.umontreal.ca> writes:
> I'd argue that the closure's enviornment should be put as the first
> element in the constants-vector rather than in a separate slot in
> the byte code object: it makes closure construction slower and more
> clostly, but it makes the function call faster.

The downside to that is that you would have to create both a new byte
code object, and a new constants vector every time a closure is
creates, e.g.:

  (defun make-closure (template env)
    (let ((args (aref template 0))
          (code (aref template 1))
          (constants (aref template 2))
          (stack-size (aref template 3))
          (doc (aref template 4))
          (interactive (aref template 5)))
      (setq constants (copy-sequence constants))
      (setq (aref constants 0) env)
      (make-byte-code args code constants stack-size doc interactive)))

Whereas if the environment is located directly in the function, you
only have to create a new byte code object:

  (defun make-closure (template env)
    (let ((args (aref template 0))
          (code (aref template 1))
          (constants (aref template 2))
          (stack-size (aref template 3))
          (doc (aref template 4))
          (interactive (aref template 5)))
      (make-byte-code args code constants stack-size doc interactive env)))

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Brinkhoff Consulting    http://www.brinkhoff.se/