I don't know if this is a common idiom, but I thought it was interesting, so I'm sharing with you.

This is a common way to return lists or references, depending on the calling context:

    sub foo {
        # ...
        return wantarray? @foo : \@foo;
    }
[download]

Now, since I was studying how to create iterators using closures, I tried this:

    sub foo {
        # ...
        return wantarray? @foo : sub { shift @foo if @foo };
    }
[download]

In other words, "return a list or an iterator": we can call the function like this:

    my @array = foo( $x );

    foreach ( @array ) {
        # do something
    }
[download]

And we can call it "iteractivelly":

    my $iter = foo( $x );

    while ( my $row = $iter->() ) {
        # do something
    }
[download]

As I said, I'm not sure if this is a common idiom (or even an useful one), but it seemed interesting so I decided to share with you. : )