On 2011-05-03, Hans Georg Schaathun <h...@schaathun.net> wrote:
> On 01 May 2011 08:45:51 GMT, Steven D'Aprano
> <steve+comp.lang.pyt...@pearwood.info> wrote:
>: Python uses a data model of "name binding" and "call by object" (also
>: known as "call by sharing"). I trust I don't need to define my terms, but
>: just in case:
>
> Without having the time to get my hand around exactly what this means:
> Simula has three ways of transmitting arguments, namely transmission
> by name, by value, and by reference. Is transmission by name the same
> as call by object?
No. For example, assume the argument is a[i].
In call by object, the expression a[i] is evaluated (i is evaluated,
and then used as an index to determine the object that is the ith
element of a). The callee's argument name is then bound to that
object.
In call by name, every time the callee references the argument name,
the expression a[i] is evaluated anew. If the value of 'i' or the
binding of 'a' has changed since the time of the function call, then
the callee's argument now refers to a different object than it did at
the time of the the function call. It's rather like a macro language
(e.g. cpp) which merely performs a textual substitution of the
argument name (the difference between pass-by-name and macro
substitution is that the context of the argument evaluation is
different).
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ROOM ...
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