By value or by reference?
joshway_without_spam at myway.com
Mon Oct 18 22:49:08 CEST 2004
Alex Martelli <aleaxit at yahoo.com> wrote:
> C is also very simple, just like Python: C always does pass by value.
> I.e., C always does implicit copy (on assignment or parameter passing),
> just like Python never does.
> So in C you ask explicitly when you want a reference (pointer) instead,
> e.g. with &foo -- in Python you ask explicitly when you want a copy
> instead, e.g. with copy.copy(foo). Two simple language, at opposite
> ends of the semantics scale, but each consistent and clean. (Python
> matches 4.5 of the 5 points which define "the spirit of C" according to
> the latter's Standard's preface...!-).
This is misleading. copy.copy does a smart, data-structure-aware copy
(not a deep copy, but exactly what copy.copy does differs among
datatypes). Parameter passing isn't about data structures; it's about
what an assignment statement means when you're assigning to a formal
parameter within a function (also possibly about some other things
like lazy evaluation), for example whether the argument list is a
declaration of new variables or just a set of aliases for other
pre-existing values (I don't say "variables" here because the value
passed in may be anonymous).
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