B.pm6

class A {
has $.data;
submethod BUILD(*@args) {
	#
}
method foo() {
	say "foo";
}
}
class B {
has $.a handles <foo>;
submethod BUILD(*@args) {
	$!a = A.new;
}
method bar() {
	say "bar";
}
}

C.pm6

class C {
use B;
has $.b handles <bar foo>;
submethod BUILD(*@args) {
	$!b = B.new;
}
}