Jan Dubois <> wrote:
> On Wed, 07 Dec 2005, Jan Dubois wrote:
>> Or you can define a normal subroutine:
>>
>> sub DATA_COLS () { $os eq 'X') ? 6 : 7 }
>>
>> assuming $os will not change during the lifetime of your program.
>
> I just realize that I should have emphasized the importance of
> specifying the empty prototype for the "constant" function. This
> makes a big difference when you use it without parentheses:
>
> my $foo = DATA_COLS + 1;
>
> will be compiled as
>
> my $foo = DATA_COLS() + 1;
>
> If you didn't specify the prototype:
>
> sub DATA_COLS { $os eq 'X') ? 6 : 7 }
>
> then it would be compiled as
>
> my $foo = DATA_COLS(+ 1);
>
> effectively ignoring the "+ 1" part.
>
> Demo:
>
> C:\>perl -we"sub foo {5}; print foo + 1"
> 5
> C:\>perl -we"sub foo () {5}; print foo + 1"
> 6
I was going to do the "there are few occasions when a subroutine
prototype is necessary, but this is one of them" speech, but you beat me
to it.
Just to add that the original request sounded more like a readonly
variable than a constant. I which case the Readonly module (and perhaps
it's friend Readonly::XS) might be worth investigating.
HTH
--
Brian Raven
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