Re: [Boston.pm] catenation of undef with string, 2 cases

I think Uri and Ricky have it nailed.

You can
wrap with do{ no warnings; ...  }  or
protect the concatenation with  42 . ($b//q()); or equivalent ?: or or
use $b .= 42 ; if order doesn't matter (it usually does, though)
or initialized $b to '' instead of undef, knowing it will be
concatenated (but in that case be sure it's tested for Truth not
Definedness)



On Wed, Nov 9, 2016 at 1:46 PM, Uri Guttman <[email protected]> wrote:
> On 11/09/2016 01:40 PM, Morse, Richard E.,MGH wrote:
>>>
>>> On Nov 9, 2016, at 12:49 PM, Mike Small <[email protected]> wrote:
>>>
>>>
>>> #!/usr/pkg/bin/perl
>>> use warnings;
>>>
>>> my $a;
>>> $a .= '70';
>>> my $b;
>>> $b = 42 . $b;
>>> print "$a, $b\n";
>>>
>>>
>>> With the script above I get an uninitialized value warning from perl
>>> 5.24 for the second concatenation but not the first. Is there a story
>>> behind this? Something to do with the first case being something you'd
>>> likely want to do without whinging from the interpreter?
>>
>> Interestingly, if you swap the order of the second concatenation, you
>> don’t get the warning, which makes it consistent.
>>
>> I don’t know if this is the reason, but here’s a place this would be
>> somewhat useful:
>>
>>         ...
>>         my $out;
>>         foreach my $k (sort keys %h) {
>>                 $out .= “$k: $h{$k}\n”;
>>         }
>>         ...
>>
>> otherwise, you have to start with:
>>
>>         my $out = ‘’;
>>
>> (admittedly, that’s how I always start this, but it’s interesting to note
>> that I could leave out the assignment to ‘’.)
>>
>>
> appending to undef is handled like incrementing (or +=) an undef. it is too
> common and useful to trigger a warning. not requiring initialization to ''
> or 0 saves a lot of code. note that this is especially true with data
> structures. $href->{text} .= $stuff is very useful. if i had to initialize
> it to '' beforehand i would hate it.
>
> this works for .= += and ++ (maybe some other things but those are the
> primary ones).
>
> uri
>
>
>
>
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-- 
Bill Ricker
[email protected]
https://www.linkedin.com/in/n1vux

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