Programming Perl, 4th Edition

The method Attribute

The method attribute can be used by itself:

sub afunc : method { ... }

Currently, this only has the effect of marking the subroutine so as not to trigger the “Ambiguous call resolved as CORE::%s” warning. (We may make it mean more someday.)

The attribute system is user-extensible, letting you create your own attribute names. These new attributes must be valid as simple identifier names (without any punctuation other than the “_” character). They may have a parameter list appended, which is currently only checked for whether its parentheses nest properly.

Here are examples of valid syntax (even though the attributes are unknown):

sub fnord (&\%) : switch(10,foo(7,3))  :  expensive;
sub plugh () : Ugly('\(") :Bad;
sub xyzzy : _5x5 { ... }

Here are examples of invalid syntax:

sub fnord : switch(10,foo();  # ()–string not balanced
sub snoid : Ugly("(");        # ()–string not balanced
sub xyzzy : 5x5;              # "5x5" not a valid identifier
sub plugh : Y2::north;        # "Y2::north" not a simple identifier
sub snurt : foo + bar;        # "+" not a colon or space

The attribute list is passed as a list of constant strings to the code that associates them with the subroutine. Exactly how this works (or doesn’t) is highly experimental. Check attributes(3) for current details on attribute lists and their manipulation.