in reply to Raku question: "Moose is Perl", but it sure ain't Raku.

The submethod BUILD is (indirectly) called by .bless. It is meant to set private and public attributes of a class and receives all names attributes passed into .bless. The default constructor .new defined in Mu is the method that invokes it. Given that public accessor methods are not available in BUILD, you must use private attribute notation instead.
C&P, straight from the docs
class C { has $.attr; submethod BUILD (:$attr = 42) { $!attr = $attr }; };; attr => 666 ); # 42 # 666
The difference between BUILD and TWEAK (as mentioned by anonymous monk below) is, that the former happens while the object is constructed, whereas TWEAK happens after that, when the object has been fully constructed.


You can lead your users to water, but alas, you cannot drown them.

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Re^2: Raku question: "Moose is Perl", but it sure ain't Raku.
by Anonymous Monk on Feb 12, 2020 at 20:22 UTC
    class A { has $.a; method TWEAK(:$!a = "foo") { } } dd; # => "foo") dd => "bar"); # => "bar")