On Nov 14, 1:11 am, shlo...@iglu.org.il (Shlomi Fish) wrote:
> Hi Charles,
>
> On Sunday 14 November 2010 01:47:36 C.DeRykus wrote:
>
> > On Nov 11, 11:27 pm, c...@pobox.com (Chap Harrison) wrote:
> > Not lots shorter but you could use a closure to hide
> > the calculation:
>
> > my $mask;
> > for my $flags ( ... ) {
> > $mask = sub { return ($flags & $_[0]) == $_[0] }
> > unless $mask;
> > given( $flags ) {
> > when ( $mask->($one_and_three) ) { ... }
> > when ( $mask->($zero_and_four) ) { ... }
> > ...
> > }
> > }
>
> This won't work properly because the closure traps the initial value of
> "$flags". For example:
>
> [code]
> #!/usr/bin/perl
>
> use strict;
> use warnings;
>
> my $closure;
>
> foreach my $name (qw(Sophie Jack Charles Dan Rachel))
> {
> $closure = sub { print "Hello $name!\n" ; } unless $closure;
>
> $closure->();}
>
> [/code]
>
> This prints "Hello Sophie!" five times. Either redeclare the closure on every
> iteration, or declare it once while using a more outer lexical variable.
Right... or simply get rid of the statement qualifier
'unless $closure' which'll work too and is what you'll
have to do in any case.
(technically, you could declare 'my $closure' both
in/outside the loop leaving the statement qualifier
as is but that's horrible )
You could just 'my $closure' solely inside the loop
too.
Declaring once outside the loop with an outer lexical
seems less satisfactory since it loosens the 'tightest
lexical scope' best practice.
--
Charles DeRykus
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