attributes

📦 min

The machinery behind sub foo : lvalue method { ... } and my $x : Shared.

Perl attaches attributes to subs and variables in three ways, and this module is the meeting point for all of them:

• Built-in attributes that Perl itself consumes — lvalue, method, const, prototype(...) on subs, shared on variables. These flip flags on the CV (or set a prototype string) and never leave the core.

• User-defined attributes — any name Perl doesn’t recognise is handed off to MODIFY_${type}_ATTRIBUTES in the caller’s package. If that handler rejects an attribute (or is absent), the declaration is a fatal error. FETCH_${type}_ATTRIBUTES is the read-side counterpart.

• A query API — attributes::get($ref) returns the combined built-in + user-defined attribute list for a referent; reftype is kept here as a backward-compatible alias for builtin::reftype.

Attribute syntax is parsed by perl and the resulting list arrives here via use attributes PACKAGE, \&sub, @attrs — see the upstream attributes POD for the full compile-time expansion.

Functions

Query

get

List every attribute set on a referent — both the built-ins Perl recognises and any package-defined ones returned by a FETCH_${type}_ATTRIBUTES handler.

reftype

Return the underlying storage type of a reference, ignoring any class it’s been blessed into.

Low-level

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.

fetch_attrs

Return the built-in attributes currently set on a referent.

guess_stash

Work out which package a reference “belongs to”, for the purpose of looking up FETCH_${type}_ATTRIBUTES / MODIFY_${type}_ATTRIBUTES.