Re: Design Question: Subclass-specific Constants
Hi Shlomi, 2. A more philosophical reason (and more major) is that I feel that "has()" > fields, which are stored inside the object's instance are *instance-based > data* while what I'm looking for is global class/subclass-based data and > constants. > I've used MooseX::ClassAttribute for errr.. class attributes: class_has '_parameter_name' => ( ... ); which seems to addess the philosophical differences between instance and class attributes (i.e. optimisation aside, IMO it improves code readability). Cheers, -- Ian Sillitoe
Re: Design Question: Subclass-specific Constants
On Tuesday 27 Apr 2010 19:17:25 Dave Rolsky wrote:
> On Tue, 27 Apr 2010, Shlomi Fish wrote:
> > Wouldn't it mean that perl will call the _build_paragraph_name of the
> > sub- class upon every instantiation of an object? I could be prematurely
> > micro- optimising in thinking that it matters, though.
>
> Yes, you are prematurely optimizing.
>
True, however, there are different reasons why I dislike having such a
class/type-based constant as a has field:
1. One can mutate it in the instance (including at run-time) by assigning to
$self->{_bold_tag_name}.
2. A more philosophical reason (and more major) is that I feel that "has()"
fields, which are stored inside the object's instance are *instance-based
data* while what I'm looking for is global class/subclass-based data and
constants.
As a result, I think I'll go with my original way, but maybe use "required ''"
to make sure such a method is defined in the non-abstract and production-ready
subclasses.
Regards,
Shlomi Fish
--
-
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God considered inflicting XSLT as the tenth plague of Egypt, but then
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Re: Design Question: Subclass-specific Constants
On Tue, 27 Apr 2010, Shlomi Fish wrote:
Wouldn't it mean that perl will call the _build_paragraph_name of the sub-
class upon every instantiation of an object? I could be prematurely micro-
optimising in thinking that it matters, though.
Yes, you are prematurely optimizing.
As an aside, naming an attribute with a name starting with "get" is an
abomination. If you want PBP style accessors, use MooseX::FollowPBP.
Attribute names should be nouns, not verbs.
Well, first of all, I used _get_ here in my code as a clarification because I
used it in the sub-class-mutated-constant-method previously. I realise it's
not wise to use _get_something() for attributes/properties/fields/object-
members/etc. (like has '_get_something'). Otherwise you can have code like
'$self->_get_something("New Value");'.
That put aside, I sometimes prefix methods returning calculations (not object
properties) with "get_" or "calc_". Whether *that* is a good idea, is much
more of a colour of the bike shed argument, and it probably doesn't matter too
much.
Right, _methods_ should be verbs, and attributes (declared with "has")
should be nouns.
-dave
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Re: Design Question: Subclass-specific Constants
On Tuesday 27 Apr 2010 18:54:06 Dave Rolsky wrote:
> On Tue, 27 Apr 2010, Shlomi Fish wrote:
> > [code]
> > has '_get_paragraph_tag_name' => (is => 'ro', default => "para");
> > [/code]
> >
> > And maybe specialise it further using «has '+_get_paragraph_tag_name'»,
> > but it seems like it would be much more verbose.
>
> I would do this ...
>
> has _paragraph_name => ( is => 'ro', builder => '_build_paragraph_name'
> );
>
> Then in the parent class:
>
> sub _build_paragraph_name {
> die 'This method must be overridden in the child'
> }
>
Wouldn't it mean that perl will call the _build_paragraph_name of the sub-
class upon every instantiation of an object? I could be prematurely micro-
optimising in thinking that it matters, though.
> As an aside, naming an attribute with a name starting with "get" is an
> abomination. If you want PBP style accessors, use MooseX::FollowPBP.
> Attribute names should be nouns, not verbs.
Well, first of all, I used _get_ here in my code as a clarification because I
used it in the sub-class-mutated-constant-method previously. I realise it's
not wise to use _get_something() for attributes/properties/fields/object-
members/etc. (like has '_get_something'). Otherwise you can have code like
'$self->_get_something("New Value");'.
That put aside, I sometimes prefix methods returning calculations (not object
properties) with "get_" or "calc_". Whether *that* is a good idea, is much
more of a colour of the bike shed argument, and it probably doesn't matter too
much.
Regards,
Shlomi Fish
--
-
Shlomi Fish http://www.shlomifish.org/
"The Human Hacking Field Guide" - http://shlom.in/hhfg
God considered inflicting XSLT as the tenth plague of Egypt, but then
decided against it because he thought it would be too evil.
Please reply to list if it's a mailing list post - http://shlom.in/reply .
Re: Design Question: Subclass-specific Constants
On Tue, 27 Apr 2010, Hans Dieter Pearcey wrote:
On Tue, 27 Apr 2010 10:54:06 -0500 (CDT), Dave Rolsky wrote:
has _paragraph_name => ( is => 'ro', builder => '_build_paragraph_name' );
Then in the parent class:
sub _build_paragraph_name {
die 'This method must be overridden in the child'
}
Alternately, turn your parent class into a role that contains
_gen_paragraph_tag and requires _build_paragraph_name. This has the advantage
of failing immediately when composed into a class without the required method,
instead of dying at runtime when it's called.
I agree, that's much better.
-dave
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Re: Design Question: Subclass-specific Constants
- Original Message
> From: Dave Rolsky
> I would do this ...
> has _paragraph_name => ( is => 'ro', builder => '_build_paragraph_name' );
> Then in the parent class:
> sub _build_paragraph_name {
> die 'This method must be overridden in the child'
>}
Why not just define a "paragraph" role which requires this? Have it be an
interface for composition-time safety (or add extra methods which might need to
be shared).
package Role::Paragraph;
use Moose::Role;
requires '_parapgraph_name';
# ...
1;
Cheers,
Ovid
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Re: Design Question: Subclass-specific Constants
On Tue, 27 Apr 2010 10:54:06 -0500 (CDT), Dave Rolsky wrote:
> has _paragraph_name => ( is => 'ro', builder => '_build_paragraph_name' );
>
> Then in the parent class:
>
> sub _build_paragraph_name {
> die 'This method must be overridden in the child'
> }
Alternately, turn your parent class into a role that contains
_gen_paragraph_tag and requires _build_paragraph_name. This has the advantage
of failing immediately when composed into a class without the required method,
instead of dying at runtime when it's called.
hdp.
Re: Design Question: Subclass-specific Constants
On Tue, 27 Apr 2010, Shlomi Fish wrote:
[code]
has '_get_paragraph_tag_name' => (is => 'ro', default => "para");
[/code]
And maybe specialise it further using «has '+_get_paragraph_tag_name'», but it
seems like it would be much more verbose.
I would do this ...
has _paragraph_name => ( is => 'ro', builder => '_build_paragraph_name' );
Then in the parent class:
sub _build_paragraph_name {
die 'This method must be overridden in the child'
}
As an aside, naming an attribute with a name starting with "get" is an
abomination. If you want PBP style accessors, use MooseX::FollowPBP.
Attribute names should be nouns, not verbs.
-dave
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http://VegGuide.org http://blog.urth.org
Your guide to all that's veg House Absolute(ly Pointless)
*/
