modify_attrs#

Apply a list of attributes to a referent and return the ones Perl didn’t recognise, so the caller can hand them to a user-defined MODIFY_${type}_ATTRIBUTES handler.

Synopsis#

my @unknown = attributes::_modify_attrs(\&foo, 'lvalue', 'Bent');

## 'lvalue' consumed internally; 'Bent' returned for package dispatch.

What you get back#

The list of attribute names that weren’t built-in. Built-in attributes (lvalue, method, const, prototype(...) for subs; shared for variables) are applied to the referent directly and do not appear in the returned list.

Examples#

## Mark a sub as lvalue, no leftovers:

sub s :lvalue { $x }
my @left = attributes::_modify_attrs(\&s, 'lvalue');   # ()

## Install a prototype via attribute:

sub p { }
attributes::_modify_attrs(\&p, 'prototype($$)');       # ()

## Custom attribute flows through:

my @left = attributes::_modify_attrs(\&s, 'MyTag');    # ('MyTag')

Edge cases#

  • Called with zero args or a non-reference first arg: croaks with Usage: attributes::_modify_attrs(@attributes).

  • A prototype( attribute without a closing ) croaks with Unterminated attribute parameter in attribute list.

  • -shared on a non-sub referent croaks with A variable may not be unshared.

Differences from upstream#

  • lvalue is always consumed as a built-in on CODE referents; the “already-defined subroutine” warning dispatch lives in attributes.pm and is not mirrored inside this XS entry.

See also#

  • _fetch_attrs — read-side counterpart, returns built-in attrs only.

  • get — public API: _fetch_attrs plus FETCH_${type}_ATTRIBUTES.

  • _guess_stash — used by get to locate the owning package.