That's a good question and a good answer. Raku (like perl) has some niceties as you dig in ... but the defaults are set at "easy"

Consider this...

use v6; 

class Point {
    has $.x is rw = 0;
    has $.y is rw = 0;

    method gist { "[$.x, $.y]" }

    method set( :$joe = $.x, :$susan = $.y ) { 
    #method set( :$joe = $!x, :$susan = $!y ) { 
        $.x = $joe; 
        $.y = $susan;
    }   
}

class Pixel is Point {
    has Int $.x is rw = 0;
    has Int $.y is rw = 0;
    has $.color = '#000000';
}

my $point = Pixel.new();
#my $point = Point.new();
say $point.x;   # 0 
say $point;    # [0, 0]
# $point.x = 3;  Error!

$point = Pixel.new(x => 3, y => 5); 
#$point = Point.new(x => 3, y => 5); 
say $point;  # [3,5]

$point.set(joe => 10, susan => 20);
say $point;  # [10, 20] 

$point.set(joe => 100);
say $point;  # [100, 20]

[download]

The $!x / $!y variant does not work because it directly refers to the PRIVATE ATTR of the Point class. But, in this case, we have used inheritance to override the Point x/y with Pixel x/y. So, when you need to reach for inheritance then the $.x / $.y variants help ... since they are the same as saying self.x and self.y - ie. they route via the settor / getter METHODS.

We need the 'is rw' to ask raku to make a settor method so that $.x = $joe; $.y = $susan; can use the assignment operation to set attr values

In reply to Re^3: Raku classes: syntax question by p6steve
in thread Raku classes: syntax question by 7stud

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