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10.8. Skipping Selected Return Values
10.8.1. Problem
You have a function that returns many
values, but you only care about some of them. The
stat function is a classic example: you often want
only one value from its long return list (mode, for instance).
10.8.2. Solution
Either assign to a list that has undef in some
positions:($a, undef, $c) = func( );
or else take a slice of the return list, selecting only what you want:($a, $c) = (func( ))[0,2];
10.8.3. Discussion
Using dummy temporary variables is wasteful; plus it feels artificial
and awkward:($dev,$ino,$DUMMY,$DUMMY,$uid) = stat($filename);
A nicer style is to use undef instead of dummy
variables to discard a value:($dev,$ino,undef,undef,$uid) = stat($filename);
Or you can take a slice, picking up just the values you care about:($dev,$ino,$uid,$gid) = (stat($filename))[0,1,4,5];
If you want to put an expression into list context and discard all of
its return values (calling it simply for side effects), you can
assign this to the empty list:( ) = some_function( );
This last strategy is rather like a list
version of the scalar operator—it calls the
function in list context, even in a place it wouldn't otherwise do
so. You can get just a count of return values this way:$count = ( ) = some_function( );
or you can call it in list context and make sure it returns some
non-zero number of items (which you immediately discard) like this:if (( ) = some_function( )) { .... }
If you hadn't assigned to the empty list, the Boolean context of the
if test would have called the function in scalar
context.
10.8.4. See Also
The section on "List Values and Arrays" in Chapter 2 of
Programming Perl and
perlsub(1); Recipe 3.1
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| 10.7. Passing by Named Parameter |  | 10.9. Returning More Than One Array or Hash |
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