[tpm] Is there a three-way version of...

[Alexandru Capsa]

In another words:

$a // $b

same as

defined $a ? $a : $b

The operator was added in Perl 5.10.0

http://perldoc.perl.org/perldelta.html




On Fri, May 29, 2009 at 4:20 PM, Mike Stok <mike at stok.ca> wrote:

>
> On May 29, 2009, at 4:17 PM, Madison Kelly wrote:
>
>  Mike Stok wrote:
>>
>>> On May 29, 2009, at 4:01 PM, G. Matthew Rice wrote:
>>>
>>>> Madison Kelly <linux at alteeve.com> writes:
>>>>
>>>>> a table-like way is adviced.
>>>>>> my $title = $condition1 ? 'result1'
>>>>>>            : $condition2 ? 'result2'
>>>>>>            : $condition 3 ? 'result3'
>>>>>>           # ... more lines here
>>>>>>
>>>>>
>>>> Yuch.  Looks like C :)
>>>>
>>>> Mine looks similar to another one I saw:
>>>>
>>>>  my $title = {aa => 'bing', bb => 'bang'}->{$key} || 'bong';
>>>>
>>> Or even use // there if your perl is recent enough, in case you ever
>>> might have cases involving false but defined strings.
>>>  my $title = { aa => 'bing', bb => 'bang', cc => '0', dd => '' }->{$key}
>>> // 'bong';
>>> Mike
>>>
>>
>> I'm not familiar with the '//' operator. It is ... ?
>>
>> Madi
>>
>
> As of perl 5.10 (I think) it is the "defined or" operator which only
> returns the right hand side if the left hand side is undef, from perlop:
>
>       C−style Logical Defined‐Or
>
>       Although it has no direct equivalent in C, Perl’s "//" operator is
>       related to its C−style or.  In fact, it’s exactly the same as "||",
>       except that it tests the left hand side’s definedness instead of its
>       truth.  Thus, "$a // $b" is similar to "defined($a) || $b" (except
> that
>       it returns the value of $a rather than the value of "defined($a)")
> and
>       is exactly equivalent to "defined($a) ? $a : $b".  This is very
> useful
>       for providing default values for variables.  If you actually want to
>       test if at least one of $a and $b is defined, use "defined($a //
> $b)".
>
>       The "||", "//" and "&&" operators return the last value evaluated
>       (unlike C’s "||" and "&&", which return 0 or 1).
>
> Mike
>
> --
>
> Mike Stok <mike at stok.ca>
> http://www.stok.ca/~mike/ <http://www.stok.ca/%7Emike/>
>
> The "`Stok' disclaimers" apply.
>
>
>
>
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>



-- 
Alexandru Capsa
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