How can I reference an existing method in Raku?

Question

As explained in the docs, you can reference an existing function by prepending the & sigil:

&say       # reference to the `say` function
&infix:<+> # reference to the infix `+` operator

How do I do this for methods?

Lorikeet

Answer 1

This article's author explains there are a few possibilities to get hold of a method object, however the most relevant one here is to use the MOP method .^lookup:

say Array.^lookup('push').raku

#`«
proto method push ($: |) {*}
»

For example to get all the candidates's signatures for Array's push method you'd do:

.say for Array.^lookup('push').candidates.map(*.signature);

#`«
(Any:U \SELF: |values)
(Array:D: Slip \value, *%_ --> Array:D)
(Array:D: \value, *%_ --> Array:D)
(Array:D: **@values is raw, *%_ --> Array:D)
»

Lorikeet

"to get all the candidates's signatures" That may work for some methods but it's hit and miss in the general case. Per the current doc on lookup it "does not provide a full list of candidates ... if you're after something which can be invoked you probably want to use find_method [which] will use a default candidate for parametric roles, whereas lookup throws an exception ... and ... [find_method] honors FALLBACK methods, which lookup does not." (And I presume what is true for find_method is also true for find_method_qualified.) – Marciemarcile