Re: sub args as pointers or values?

[Chris Devers]

On Fri, 16 Dec 2005, Bryan R Harris wrote:

> I remember from my C++ class that when you pass arguments to 
> subroutines you can pass them either as a pointer to the real variable 
> (so you modify the original if you change it), or as a copy (which you 
> can change all you want and not affect the original).

The terminology I was taught for this was "pass by reference" to denote 
sending around pointers to the same physical memory location, and "pass 
by value" to denote sending around abstract logical pieces of 
information that are typically copies of the original variable.

Like most languages, Perl has ways to do both of these.

Normal argument passing in Perl is basically like pass by value or pass 
by copy. You don't generally have to do anything extra to get this 
behavior.

To pass a reference to a variable to a subroutine, prefix the variable 
name with a backslash: \%myhash, [EMAIL PROTECTED], etc. You can capture this 
reference into a scalar -- $hashref = \%myhash -- and then access the 
contents of the reference by dereferencing: $$hashref{"KEY"} = "VALUE";

This is explained in detail in perldoc's perlref and perlobj pages:

http://perldoc.perl.org/perlref.html
http://perldoc.perl.org/perlobj.html

It's also in books like _Learning Perl Objects, References & Modules_ 
and _Object Oriented Perl_:

http://www.oreilly.com/catalog/lrnperlorm/
http://www.amazon.com/exec/obidos/tg/detail/-/0596004788?v=glance
http://books.perl.org/book/200

http://www.manning.com/Conway/
http://www.amazon.com/exec/obidos/tg/detail/-/1884777791?v=glance
http://books.perl.org/book/171



-- 
Chris Devers

Ù³ÄCIü[Ð-Q˜

-- 
To unsubscribe, e-mail: [EMAIL PROTECTED]
For additional commands, e-mail: [EMAIL PROTECTED]
<http://learn.perl.org/> <http://learn.perl.org/first-response>