As far as I can tell, an attribute is nothing more than a label you can give to a subroutine that you can later query.

That is exactly what a subroutine attribute is. Nothing more, nothing less. If you want special behavior associated with a given label, you have to add it yourself. (:lvalue and friends have that behavior associated by Perl itself.)

I don't see much usefulness in this.

There have been several examples above for the usefulness. Basically, I think of it as meta-programming. Sometimes, you want to say that these three classes implement this interface. Sometimes, you want to say that this variable is of this class. Sometimes, you want to say that these two subroutines are special in some way.

For example, attributes are definitely useful for CGI::Application, which is why Thilosophy is working on auto-declaring runmodes. Maypole is finding it useful for a similar reason.

Me, I tend to write engines. For example, PDF::Template has a basic engine - each node in the parsetree can potentially execute something at the following stages:

Ideally, I'd like to be able to mark a given method as executing during a given stage vs. having to declare a method of a given name and having to remember to call SUPER. This way, I can potentially declare more than one method as executing during a given stage. That allows me to write clearer code, instead of catch-all subroutines.

(I can't do this, FYI, because PDF::Template has to be usable under mod_perl.)

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In reply to Re: How Are Attributes Useful? by dragonchild
in thread How Are Attributes Useful? by Limbic~Region

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