Re: How Are Attributes Useful?

I recall you have been studying the :lvalue attribute for subs. Reflect that that attribute is more than a tag that you may query at runtime like some kind of metadata. I'm not sure how I'd go about querying that.

When the :lvalue attribute is applied to a sub, it changes how the sub is compiled and what usage is permitted of it.

The description of attributes as tags to be queried sounds a lot like the "properties" Lisp can attach to a symbol. I think that's a mischaracterization.

A read of the Attribute::Handlers pod suggests that magic outside runtime is what attributes are for. Those docs give some non-trivial examples. I suspect that perldoc -m Attribute::Handlers will yield lots of wisdom on the matter, but I know for a fact it won't be easy ;-)

I'm sure that perl attributes would benefit from more of us experimenting with them.

After Compline,
Zaxo

Comment on Re: How Are Attributes Useful?

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Re^2: How Are Attributes Useful? by Limbic~Region (Chancellor) on Jan 19, 2005 at 00:58 UTC
Zaxo, Reflect that that attribute is more than a tag that you may query at runtime like some kind of metadata. I'm not sure how I'd go about querying that. Really. I haven't found a single example of how one might modify the behavior of a subroutine using attributes outside the few built-ins. As far as querying the attributes - it was in the synopsis of perldoc attributes `use attributes (); # optional, to get subroutine declarations my @attrlist = attributes::get(\&foo);` [download] I have looked at Attribute::Handlers and still felt unsatisfied. Attribute::Handlers::Prospective looks promising after glancing at the documentation but I find it hard to believe that there are no code examples outside the module. Why is this I wonder. It seems to me that you are right - the majority of us are in the dark and so attributes, if useful at all as others have implied, are way underdeveloped in perl. Cheers - L~R	[reply] [d/l]
Re^3: How Are Attributes Useful? by redlemon (Hermit) on Jan 19, 2005 at 22:27 UTC
Check Bot-CPAN. It's Glue module uses Attribute::Handlers to define well.. attributes to methods. That lets you define a bot command like: `sub list :help ("lists available modules") :private :adminCmd { # implements list() }` [download] I thought that was a rather elegant way of doing this.	[reply] [d/l]
Re^2: How Are Attributes Useful? (just tags) by tye (Sage) on Jan 18, 2005 at 23:02 UTC
No, they are just text tags. Perl checks for the "lvalue" tag and, if found, does special processing. But the attribute is just a way to tell Perl to do that special processing. - tye	[reply]
Re^3: How Are Attributes Useful? (just tags) by Zaxo (Archbishop) on Jan 19, 2005 at 00:32 UTC
That's an implementation detail. The point is that thay represent metadata for the perl compiler, not the user's runtime. It's magic, I say! After Compline, Zaxo	[reply]
Re^4: How Are Attributes Useful? (just tags) by tye (Sage) on Jan 19, 2005 at 01:57 UTC
s/not/or/ Attributes are just syntactic sugar for implementation details. If you think attributes are the magic, then you'll never understand how to use attributes in general. - tye	[reply]