gistfile1.txt

class FreezeHash {
    has $.hash handles *;
    method new(*@args) { self.bless: *, hash => Hash.new: @args }
    method at_key(FreezeHash:D: $key is copy) is rw {
        $!hash.exists($key) or warn "Cannot set non-existing key '$key'";
        $!hash.at_key($key);
    }
}
 
my $fh = FreezeHash.new: "a" => 1, "b" => 2;
say $fh.perl;
 
say $fh<a>;
$fh<c> = 3;
say $fh<c>;