Re: Assignment to a value only if it is defined

If bar() is a complex function, then perhaps it should be the one returning the default value...

If that's not reasonable, then perhaps you need a default wrapper or something... Here's two ideas:

sub mybar {
   my $t = bar();
   return "default" unless defined $t;
   return $t;
}

sub default {
    my $to_call = shift;
    my $default = shift;
    my $t = to_call->(@_);
    return $default unless defined $t;
    return $t;
}
[download]

Or just do what the others said above (5.10+ only): $x = bar() // "default";

-Paul

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Re^2: Assignment to a value only if it is defined by voj (Acolyte) on Jan 20, 2010 at 15:44 UTC
The "default" action is not to do a assignement at all. But using the current value of $foo will do it as JavaFan suggested: `$foo = $bar // $foo;` However this is not much better then `$foo = $bar if defined $bar;` Because the other part of the statement ($foo) is duplicated - if I have a long variable like $myhash{mykey}->{mykey2} instead of $foo it only gets uglier. I was looking for a simple and short syntax like: `$foo =// $bar` But appereantly such operator does not exist in Perl. The best solution I found so far (also ugly but not getting more complex if $foo and $bar are long expressions) is: `{local $_ = $bar; $foo = $_ if defined $_;}` [download]	[reply] [d/l] [select]
Re^3: Assignment to a value only if it is defined by jdporter (Canon) on Jan 20, 2010 at 16:40 UTC
Because the other part of the statement ($foo) is duplicated - if I have a long variable like $myhash{mykey}->{mykey2} instead of $foo it only gets uglier Then try: `$_ = $bar // $_ for $myhash->{mykey}{mykey2};` [download]	[reply] [d/l]
Re^3: Assignment to a value only if it is defined by ikegami (Pope) on Jan 20, 2010 at 19:02 UTC
`{local $_ = $bar; $foo = $_ if defined $_;}` `$foo = $_ for grep defined, expensive();` [download]	[reply] [d/l] [select]


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