I've been playing with code attributes lately. I'm using them to annotate
introspection hints on functions used for commands in an interactive
system. These annotations give help text, hints on argument parsing,
etc.. I've found Attribute::Handlers doesn't work for these because my
program dynamically reloads the code all the time, whenever things
change. It doesn't cope with them.
So, I wrote [the attached]. Not quite sure what name to call it - All the
rest in Attribute:: space seems to be specific attributes written using
Attribute::Handlers. That said, I can't find anywhere else more suited.
Thoughts, anyone? On the name, the implementation, the idea,.. anything
else that comes to mind?
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Attribute::Storage(3pmUser Contributed Perl DocumentatiAttribute::Storage(3pm)
NAME
Attribute::Storage - store and access named attributes about CODE
references
SYNOPSIS
package My::Package;
use Attribute::Storage;
sub Title : ATTR(CODE)
{
my $package = shift;
my ( $title ) = @_;
return $title;
}
1;
package main
use Attribute::Storage qw( get_subattr );
use My::Package;
sub myfunc : Title('The title of my function')
{
...
}
print Title of myfunc is: .get_subattr(\myfunc, 'Title').\n;
DESCRIPTION
This package provides a base, where a package using it can define
handlers for particular code attributes. Other packages, using the
package that defines the code attributes, can then use them to annotate
subs.
This is similar to Attribute::Handlers, with the following key
differences:
· Attribute::Storage will store the value returned by the attribute
handling code, and provides convenient lookup functions to retrieve
it later. Attribute::Handlers simply invokes the handling code.
· Attribute::Storage immediately executes the attribute handling
code at compile-time. Attribute::Handlers defers invocation so
it can look up the symbolic name of the sub the attribute is
attached to. An upshot here is that the invoked code in
Attribute::Storage does not know the name of the sub it attaches
to.
· Attribute::Storage is safe to use on code that will be reloaded,
because it executes handlers immediately. Attribute::Handlers
will only execute handlers at defined phases such as BEGIN or
INIT, and cannot reexecute the handlers in a file once it has
been reloaded.
ATTRIBUTES
Each attribute that the defining package wants to define should be done
using a marked subroutine, in a way similar to Attribute::Handlers.
When a sub in the using package is marked with such an attribute, the
code is executed, passing in the arguments. Whatever it returns is
stored, to be returned later when queried by get_subattr or
get_subattrs.
sub AttributeName : ATTR(CODE)
{
my $package = shift;
my ( $attr, $args, $here ) = @_;
...
return $value;
}
At attachment time, the optional string that may appear within brackets
following the attribute’s name is parsed as a Perl expression in array
context. If this succeeds, the values are passed in a list to the
handling code. If this fails, an error is returned to the perl
compiler. If no string is present, then an empty list is passed to the
handling code.
package Defining;
sub NameMap : ATTR(CODE)
{
my $package = shift;
my @strings = @_;
return { map { m/^(.*)=(.*)$/ and ( $1, $2 ) } @strings };
}
package Using;
use Defining;
sub somefunc : NameMap(foo=FOO,bar=BAR,splot=WIBBLE) { ... }
my $map = get_subattr(somefunc, NameMap);
# Will yield:
# { foo = FOO,
#bar = BAR,
#splot = WIBBLE }
Note that it is impossible to distinguish
sub somefunc : NameMap { ... }
sub somefunc : NameMap() { ... }
FUNCTIONS
$attrs = get_subattrs( $sub )
Returns a HASH reference containing all the attributes defined on the
given sub. The sub should either be passed as a CODE reference, or as a
name in the caller’s package. If no attributes are defined, a reference
to an empty HASH is returned.
$value = get_subattr( $sub, $attrname )
Returns the value of a single named attribute on the given sub. The sub
should either be passed as a CODE reference, or as a name in the
caller’s package. If the attribute is not defined, undef is returned.
AUTHOR
Paul Evans [EMAIL PROTECTED]
perl v5.10.0 2008-10-20 Attribute::Storage(3pm)
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--
Paul LeoNerd Evans
