[Purdue-pm] Subroutine Attributes, or it's all my fault.

[Dave Jacoby]

Duh!

while ( my $ii = $i->iterate ) {}

is judged on $ii, and if $ii == 0, it is based on the value of $ii , not of
defined $ii.

So while (1) {
   my $ii = $i->iterate;
  ...
}

On Tue, Aug 21, 2018 at 11:57 AM Dave Jacoby <jacoby.david at gmail.com> wrote:

> I won't start in on why I started looking at attributes (blame Matt S.
> Trout), but
> in looking at them, PerlTricks has a post showing how you can assign to a
> function like a variable by setting lvalue.
>
> I played with it some to get this:
> package Foo;
> use Scalar::Util qw(looks_like_number);
> sub new { bless {}, shift }
> sub iterate : lvalue {
> my $self = shift;
> $self->{iterate} = 0
> if !defined $self->{iterate}
> || !looks_like_number( $self->{iterate} );
> $self->{iterate} ++ ;
> $self->{iterate};
> }
>
> This allows this:
>
> my $i = Foo->new();
> $i->iterate = 11;
> while ( my $ii = $i->iterate ) {
> say qq{\t$ii} ;
> last if $ii >= 20;
> }
>
> Which gives us this:
>
> 12
> 13
> 14
> 15
> 16
> 17
> 18
> 19
> 20
>
> To reiterate, you would expect $i->iterate(11), not $i->iterate = 11 .
>
> This is a small change, and I might not ever use this in real life --
> esp., if mst said (I think) that there's a problem with signature and
> attribute order recently, meaning I couldn't write sub function ( $x ) {
> code } anymore.
>
> But...
>
> my $i = Foo->new();
> $i->iterate = -4;
> while ( my $ii = $i->iterate ) {
> say qq{\t$ii} ;
> last if $ii >= 20;
> }
>
> gives use
>
> -3
> -2
> -1
>
> Something in Foo::iterate stops at 0. Zero should be defined. Zero should
> look like a number.
>
> Can anyone see the "stop iterating at zero" bug in my "toy code; don't use
> in production" iterator?
> --
> Dave Jacoby
> jacoby.david at gmail.com
>
> Don't panic when the crisis is happening, or you won't enjoy it.
>


-- 
Dave Jacoby
jacoby.david at gmail.com

Don't panic when the crisis is happening, or you won't enjoy it.
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