Raku custom hash-like associative type implementation using complex type for the keys

#! /usr/bin/env raku

use v6.d;

subset CustomKey of List where .elems == 2 && .all ~~ UInt:D;

subset CustomValue of List where * ~~ (
    :foo(UInt:D)
    :bar(Str:D)
).sort;

class CustomHash does Associative[CustomValue:D, CustomKey:D] {
    has CustomValue:D %!data{Str:D};
    subset K where CustomHash.keyof;
    subset V where CustomHash.of;
    method AT-KEY(K \k --> V) { %!data{k.Str} }
    method EXISTS-KEY(K \k --> Bool:D) { %!data{k.Str}:exists }
    method ASSIGN-KEY(K \k, V \v) { %!data{k.Str} = v }
}

my CustomHash:D \a = CustomHash.new;

a{$(12,34)} = (foo => 123, bar => 'hi').sort.List;
a{$(12,34)}.raku.say; # $(:bar("hi"), :foo(123))