|Syntactic Confectionery Delight|
Re: Class::Std : How does MODIFY_HASH_ATTRIBUTES work?by xdg (Monsignor)
|on Oct 13, 2005 at 21:24 UTC||Need Help??|
It's part of the attributes mechanism. It's automatically called to handle the attributes of an appropriate type:
You might also want to browse the source of Attribute::Handlers for examples of how they get used.
Updated: expanded answer...
attributes in turn, looks for a MODIFY_*_ATTRIBUTES in the current package or the @ISA array and calls it to handle the attribute. If that function returns any attributes, those are "unhandled" attributes and the import croaks with an error.
MODIFY_*_ATTRIBUTES receives the package name, a reference to the item attributed, and a list of attributes attached. E.g. in Class::Std:
The rest of that routine checks for an "ATTR" attribute, extracts any information passed along with it, like defaults, and installs the accessors as "usual". For example:
The only "magic" here is the way that Perl automatically expands the ":ATTR" into a call to the attributes module. After that, it's just normal function calls between modules.
CAVEAT: this all happens at compile time -- so it's like a BEGIN block and certain things aren't yet set up. This is why in MODIFY_CODE_ATTRIBUTES, the name and reference of the method are just pushed onto a data structure, and the actual handling of the attribute occurs later in the CHECK block, after the method has been compiled.
(This is why anything build with Class::Std won't work with mod_perl, which has no CHECK phase. You can see an approach which will work in my own experimental Object::LocalVars, which requires the module using it to make an explicit function call to give_methods which gets run after its compilation when the module is first loaded in what is effectively a BEGIN phase at that point.)
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