$foo //= $bar;

The // and //= operators will behave like || but will test for defined() rather than for truth.

-sam

$foo = defined $bar ? bar : $default_for_foo;

## could be written as, but remember, that 0 is false
$foo = $bar;
$foo ||= $default_for_foo;
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____________________________________________________
** The Third rule of perl club is a statement of fact: pod is sexy.

These two are not exactly the same... they will behave differently if $bar is defined but has a non-true value (like 0). That's because the || operator tests for truth, while the much-to-be-desired // operator (in Perl6) will test for defined-ness. So in Perl6, you could write it as:

$foo = $bar;
$foo //= $default_for_foo;
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or, I imagine, like this:

$foo = $bar // $default_for_foo;
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-- Mike

--
just,my${.02}

While waiting for the speculated "defined" version of "||", I wrote def -- Deal nicely with undefined values. That simplifies your second case:     $foo = def( $bar, $default_for_foo ); Throwing together something for exists I came up with this:     $a = has( a=>$hashref, $default_for_a ); I replaced $foo with $hashref in my example above.

Here is what has() looks like:

sub has {
    my( $key, $hv, $val, $force )= @_;
    if(  exists $hv->{$key}  ) {
        $val= $hv->{$key};
    } elsif(  ! defined wantarray  ||  $force  ) {
        $hv->{$key}= $val;
    }
    return $val;
}
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  sub new {
      my $pkg = shift;
      my $self = { a => $default_for_a, @_ };
      bless $self, $pkg;
  }
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I do this occasionally, when establishing quick defaults. Testing revealed that the last defined key/value pair for a given hash is the one that is used. Is this documented anywhere?

my $self = { %defaults, @_ };

As far as I know, it's only documented in the same sense as this bit of code:

my $x;
$x = 1;
$x = 2;
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-Mark