[Tutor] defined()

[Danny Yoo]

> > I'm interested in what use you would make of such a thing?
>   My business partner is a perl programmer. He uses defined() a lot, I
>   think, I've seen it in his code....

Hello!

The common idiom in Perl, I think, is to at least declare the variable,
even if one doesn't give an initial value, like this:

    #############################################
    ## Perl pseudocode ##
    use strict;
    my $name;
    ## do things here that should initialize name
    if (! defined($name)) {
        # handle degenerate case here
    }
    #############################################


But this is very different than:

    #############################################
    ## Perl pseudocode that doesn't use strict
    ## do things here that should initialize name
    if (! defined($name)) {
        # handle degenerate case here
    }
    #############################################

Now, if your business partner doesn't have the line 'use strict' in their
code, then give them a good kick and tell them to use it!  It's criminal
for a professonal Perl programmer not to "use strict", and I feel almost
foolish about bringing this up.  But it has to be said, just in case.
*grin*


In Python, the first assignment to a variable name has the same effect as
declaration, so the first Perl snippet has a translation like:

    #############################################
    ## Python pseudocode
    name = None
    ## do things here that should initialize name
    if name is None:
        ## handle degenerate case here
    #############################################

where we can use None as our uninitialized value.


Hope this helps!