in reply to Re^2: Method chain object with easy syntax
in thread Method chain object with easy syntax

the scalar itself is fetched only once

Is that guarenteed? If it is I almost withdraw my opinion. I say almost, because I still think it's unnecessary complicated (in that it uses a global as loop variable). If you change 

for my $pair (@$chain) {

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to the not completely unusual construct 
while (@$chain) {
    my $pair = shift @$chain;

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for whatever reason it'll demonstrate why I think this is playing with fire -- you have an extra thing to keep in mind two years later when you patch the code. As you say yourself
The important point is that the contents of the array it points to at start doesn't change
These's a general concensus that using globals like this is A Bad Thing, even if it's not such an obvious case. Not only do you have to remember that directly inside the loop not change @$chain, but you can't get the idea to assign to @$chain in &__Set_MethodChain__. That's a lot of unnecessary conditions just to not copy a presumably small array. If you copy the array you don't have anything extra to worry about and that might save yourself from future troubles. Indeed, the code works, I just get a bad feeling when I see it. :-)

if you want to build a chain of methods without the length of it known in advance, then the sub solution can be more difficult

You can easily compose new chains using other "sub chains", if that's what you're talking about. 

#!/usr/bin/perl -wl

AUTOLOAD {
    print $::AUTOLOAD =~ /.*::(.*)/s;
    $_[0];
}

my $chain1 = sub { $_[0]->m2->m3 };
my $chain2 = sub { $_[0]->m1->$chain1->m4->m5 };

main::->$chain2;

__END__
m1
m2
m3
m4
m5

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Maybe I misunderstood?

ihb

See perltoc if you don't know which perldoc to read!

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Re^4: Method chain object with easy syntax
by ambrus (Abbot) on Apr 20, 2005 at 20:05 UTC

    I agree that iterating on @$chain isn't very clean code, because $chain is a global variable. You can of course make a copy of the array @$chain in the __Call_MethodChain__ function. The change is not difficult, the new sub is this: 

    sub __Call_MethodChain__ {
        my $r = $_[0];
        my @chain = @$chain;
        for my $pair (@chain) {
                my($method, $args) = @$pair{"method", "args"};
                $r = $r->$method(@$args);
        }
        $r;
}

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    Your point with the while loop is especially valid, because my code doesn't propagate context for a method chain call. The simplest version (the one with blessed subs) doesn't have this bug. The simplest way to fix this is a looped shift like this: 

    sub __Call_MethodChain__ {
        my $r = $_[0];
        my @chain = @$chain;
        for (;;) {
                my $pair = shift @chain;
                my($method, $args) = @$pair{"method", "args"};
                0 == @chain and
                        return $r->$method(@$args);
                $r = $r->$method(@$args) ;
        }
}

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    You are right, the straightforward solution can even handle dynamic building of method chains well, and it also doesn't have the bug I've mentioned above. I can still also say that this was just an experiment I made with perl (or even just some filthy trick to get some noderep).

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