Re: scoping question

[vladb]

Declaring variables once at the beginning of the code block where they are being first used is the best practice imo. One other alternative (yet poor) approach is to use the special $_ variable.

if     ( $_ = $obj->get_id() )
{
    # use $_ inside this block...
    $obj->do_this();
}
elsif     ( $_ = $obj->create_id() )
{
    # use $_ inside this block
    $obj->do_that();
}
else
{
    $obj->do_somethingelse();
}

Generally, however, this wouldn't be a very sound approach, as it is usually very easy to loose track of the $_ variable. Although, it does spare you having to declare variables, especially for short code blocks or loops.

Update: As ikegami pointed out (++), I stress that the use of $_ is a bad idea. I just wanted to show one alternative, albeit a bad one as a means of warning against such approach. :)

[ikegami]

Don't assign to $_ without localizing it first! $_ is usually aliased to another variable, and your code would clobber it. The fix is to add local to the first assignment (as shown below). However, if you do that, you've gained nothing but obfuscation. You should use my $id instead of local $_.

if     ( local $_ = $obj->get_id() )  # XXX Use "my $id =" instead of
{                                     #     "local $_ =" for clarity.
    $obj->do_this();
}
elsif     ( $_ = $obj->create_id() )  # XXX Use "$id =" instead of
{                                     #     "$_ =" for clarity.
    $obj->do_that();
}
else
{
    $obj->do_somethingelse();
}