On Apr 20, 2:11 pm, dery...@gmail.com ("C.DeRykus") wrote:
> On Apr 20, 9:38 am, jimsgib...@gmail.com (Jim Gibson) wrote:
>
> ...
> > >> If we put $x=(1,2) then we get 2 without the error message.
>
> > >> Can someone please explain why?
>
> > > Yes, perl places the last item in the list into the variable. That's
> > > why the others are "useless".
>
> > > Try:
>
> > > my $x = ( 1, 2, 'this one' );
>
> > Yes, but as srd has observed, you get one fewer warning message than there
> > are "useless" items. Try:
>
> > my $x = ( 1, 2 );
>
> > and you get no warnings. Try:
>
> > my $x = ( 1, 2, 3, 4 );
>
> > and you get 2 warnings. One of those "useless" items isn't useless (or Perl
> > just doesn't care).
>
> That makes sense since the () list op is right associative.
> The comma op is binary and would consume 3,4 without
> warning but 1,2 would then draw "useless use of a constant..."
> warnings.
>
> If, it'd been (1,$y,3,4) you'd get a "useless use of a variable..."
> as well as a "useless use of a constant..."
>
I should clarify though that () isn't a list operator but just a
grouping of n list items. The binary comma op marches
through the items and tosses the first n-2 with the warning
"useless use ...". The final two are consumed: the first is
tossed away and then the final item is evaluated and then
returned.
That's why you get n-2 warnings (with the exceptions 0,1
that were mentioned).
--
Charles DeRykus
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