Re^2: Psychic Disconnect and Object Systems

It seems like you're being deliberately obtuse in your first two answers.

How so? They didn't do anything to hinder what you want to do whatsoever.

The easiest thing to do is to use Moose's automatically-generated new, which does the thing the OP doesn't want. AFAICT "attributes" are the product of confusion between the view that an "object" is a collection of named bits of state, and the view that an "object" is a box to which you send "messages." People want "messages" telling the "object" "give me the value of this named bit of state," so "objects" have "attributes" by default.

is => 'ro' is simply a shortcut for reader => $name, and is => 'rw' is simply a shortcut for accessor => $name.

But if you just do

has 'foo';
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You get read-only attributes by default. The OP's question is "why?" The answer usually leads to a religious war.

As for internal-use attributes, the OP is wondering what this does:

package Base;
use Moose;
has 'x', default => 'Base'; # internal

sub foo {
   print shift->x;
}

package Child;
use Moose;
has 'x', default => 'Child'; # also internal

package main;
Base->new->foo;    # "Base"
Child->new->foo;   # "Base" or "Child"?
[download]

(I would test it myself, but don't have Moose lying around.)

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Re^3: Psychic Disconnect and Object Systems by ikegami (Patriarch) on Apr 15, 2011 at 17:31 UTC
The easiest thing to do is to use Moose's automatically-generated new, So? Unless you are proposing that Moose should automatically build the desired constructor instead (impossible), that's irrelevant. The only thing that matters is how easy it is to build your own constructor, and Moose doesn't hinder that at all. But if you just do `has 'foo';` You get read-only attributes by default. No you don't. You get an error. The OP's question is "why?" Obviously not. He's asking about `is=>'ro'`. ro = read-only. It seems like you're being deliberately obtuse in your first two answers. You have not identified any issues with them. As for internal-use attributes, the OP is wondering what this does: I did indeed misread that question.	[reply] [d/l] [select]
Re^4: Psychic Disconnect and Object Systems by educated_foo (Vicar) on Apr 15, 2011 at 22:16 UTC
No you don't. You get an error. Here we go... Which error? Well, let's look at the docs... has $name\|@$names => %options This will install an attribute of a given $name into the current class. If the first parameter is an array reference, it will create an attribute for every $name in the list. The %options are the same as those provided by Class::MOP::Attribute, in addition to the list below which are provided by Moose (Moose::Meta::Attribute to be more specific): is => 'rw'\|'ro' The is option accepts either rw (for read/write) or ro (for read only). These will create either a read/write accessor or a read-only accessor respectively, using the same name as the $name of the attribute. If you need more control over how your accessors are named, you can use the reader, writer and accessor options inherited from Class::MOP::Attribute, however if you use those, you won't need the is option. Looks like "has" takes a scalar and a hash of options, and "is" doesn't seem to be a mandatory option. You've got me stumped!	[reply]
Re^5: Psychic Disconnect and Object Systems by ikegami (Patriarch) on Apr 15, 2011 at 22:47 UTC
"Attribute (%s) of class %s has no associated methods (did you mean to provide an "is" argument?)" Basically, omitting "`is`" (or equivalent) doesn't make the attribute read-only, it makes it neither readable nor writable! and "is" doesn't seem to be a mandatory option Remember how I said `is` is just a shortcut for something else? It's the lack of getters that actually triggers the error.	[reply] [d/l] [select]
Re^5: Psychic Disconnect and Object Systems by ikegami (Patriarch) on Apr 15, 2011 at 22:52 UTC
"Attribute (%s) of class %s has no associated methods (did you mean to provide an "is" argument?)" Basically, omitting "`is`" (or equivalent) doesn't make the attribute read-only, it makes it neither readable nor writable! and "is" doesn't seem to be a mandatory option Remember how I said `is` is just a shortcut for something else? It's the lack of getters that actually triggers the error.	[reply] [d/l] [select]