[EMAIL PROTECTED] wrote:
> Wizards & Wise Ones,
>
> Is there a way to have a constant take on different values? I've
> tried the code below, and all I get as a value for DATA_COLS is seven.
> Always seven.
>
> use Getopt::Std;
>
> my %opts;
>
> getopts( 'o:', \%opts );
>
> my $os = $opts{'o'};
>
> use constant (DATA_COLS => (($os eq 'X') ? 6 : 7));
>
> Okay, this is apparently wrong. Is there a right way, some way I can
> set DATA_COLS to different values based on input? I can't use the
> Readonly module to create a "non-changeable variable," it's not
> installed in the target systems, just development (beats me, too, but
> that's how it is). Or must I give up the idea of having a constant and
> just let DATA_COLS become the (vanilla) variable $DATA_COLS?
You either have to put *all* the code that sets up $os into a BEGIN block
in front of your "use constant" statement.
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.
Constants are really no more than subroutines that return a constant value.
The compiler will then inline those subroutines instead of generating
function calls. So you lose a little bit of performance by calling
a real sub at runtime, but I doubt you'll actually notice.
Cheers,
-Jan
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