Why ref($proto) should be avoided

You almost got me. :)

On page 103, TheDamian explains that calling a 'constructor' as an object method is a lazy way to copy an object, but observe what happens when you change an object's attributes at runtime and try to clone it:

use strict;
use Clone qw(clone);

my $foo = foo->new();
$foo->{spam} = {spam =>'eggs'};

my $bad_clone  = $foo->new();
my $good_clone = clone($foo);

$bad_clone->{spam}->{spam}  or warn "bad has no eggs";
$good_clone->{spam}->{spam} or warn "good has no eggs";

package foo;
use strict;

sub new {
   my $class = shift;
   my $proto = ref($class) || $class;
   return bless {}, $proto;
}
[download]

TheDamian also explains on page 105 that

While many experts view the overloading of constructors as object copiers to be a natural extension of their functionality, others consider the technique unintuitive, too subtle, and more likely to produce obscure and hard-to-maintain code.

and on page 106

If you have a choice, it's probably better to code a seperate clone method. Apart from keeping your individual methods simpler and less prone to bugs, the method's name will force client code to be more clearly self-documenting.

jeffa

doesn't like spam

Comment on Why ref($proto) should be avoided Download Code

Replies are listed 'Best First'.
Re: Why ref($proto) should be avoided by frag (Hermit) on Jul 17, 2002 at 11:30 UTC
Still, that's after using ref($caller) in all the preceding examples. Ditto in the 'final version' of CD::Music (p.114). And you've got to admit, "probably better" aint much of a condemnation. -- Frag.	[reply]
(jeffa) 2Re: Why ref($proto) should be avoided by jeffa (Bishop) on Jul 17, 2002 at 14:49 UTC
Well, i wouldn't say all the preceding examples. He does use some form of ref($caller) extensively throughout the book, but not in every example. And i can admit that "probably better" ain't much of condemnation, but not as much as i can admit that it ain't much of a recomendation either. I see nothing wrong with simpler methods that are less prone to bugs and are more clearly self-documenting. :) Update: i should mention that Class::MethodMaker's `new_hash_init` specifier makes for a very robust instance constructor. Consider using it if you don't like having to write your own clone method. jeffa L-LL-L--L-LL-L--L-LL-L-- -R--R-RR-R--R-RR-R--R-RR B--B--B--B--B--B--B--B-- H---H---H---H---H---H--- (the triplet paradiddle with high-hat)	[reply]


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