Re: [MacPerl] Coding style

[Christian Brechbuehler <brech@vision.ee.ethz.ch>]

Excerpt of message (sent 4 February 1999) by Emmanuel. M. Decarie:
> I wonder how people show in their code how a subroutine is altering
> a global variable.

Your example is about altering the function argument, not a global.
You suppose

> myFunc(\@global);
> 
> or 
> 
> @global = myFunc(\@global);

I perfer the first.  Fewer keystrokes, and clean enough.  The second
will copy around all return values, if I read it right (less efficient).

> I'm always a little bit worried by what we call in French "effet de
> bord" (sorry can't find a translation)

"Side effect", quite literally.  

> at the moment is that when you pass by reference an array or a hash,
> there is nothing to show in the params that the function have the
> right to make changes to the original.

Yes, perl ist not the strictest of languages.  In your example, it is
quite obvious (from the \) that myFunc _can_ change the variable you
pass in. It would be nice to document if it _will_.

Using prototypes, you can write functions that implicitly take a
reference, without a hint in the calling code.  Many of our beloved
builtins do this, and indeed change one of their arguments, e.g.,
chop, splice, push, shift, read, s///.  That's fine; you passed the
variable explicitly.

But if these aren't given enough parameters, they work on $_, @_, or
@ARGV (!!).  Now that's what I call changing globals.  I avoid this in
any subroutine I write.

Yes, in Ada you can be more specific.  Even C++ (and now ANSI C) has
the "const" modifier.  Perl isn't rigorous.

> Is there something similar in Perl ?

You could specify it in POD :-)

	Christian Brechbuehler
	
	Communication Technology Laboratory, Image Science Group
	Swiss Federal Institute of Technology (ETH), Zurich

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