How do I declare a hash of hashes of numbers in Perl 6?

Question

A hash, by default, converts all keys to strings. This causes issues when your keys are numbers which may be close:

> my %h; %h{1/3} = 1; %h{0.333333} = 2; dd %h;
Hash %h = {"0.333333" => 2}

This can, of course, be fixed as follows:

>  my %h{Real}; %h{1/3} = 1; %h{0.333333} = 2; dd %h;
Hash[Any,Real] %h = (my Any %{Real} = 0.333333 => 2, <1/3> => 1)

But now I need a hash of hashes of numbers, e.g. { 1/3 => { 2/3 => 1, 0.666667 => 2 } }.

> my %h{Real}; %h{1/3}{2/3} = 1; %h{1/3}{0.666667} = 2; dd %h;
Hash[Any,Real] %h = (my Any %{Real} = <1/3> => ${"0.666667" => 2})

How do I fix that?

Best I can figure out is the following workaround:

> my %h{Real}; %h{1/3} //= my %{Real}; %h{1/3}{2/3} = 1; %h{1/3}{0.666667} = 2; dd %h;
Hash[Any,Real] %h = (my Any %{Real} = <1/3> => $(my Any %{Real} = <2/3> => 1, 0.666667 => 2))

but that's just annoying.

Answer 1

The following works:

my Hash[Real,Real] %h{Real};
%h{1/3} .= new;
%h{1/3}{2/3} = 1;

Which is not great.

---

The following also works as a work-around.

my Hash[Real,Real] %h{Real};
%h does role {
  method AT-KEY (|) is raw {
    my \result = callsame;
    result .= new unless defined result;
    result
  }
}

%h{1/3}{2/3} = 1;

say %h{1/3}{2/3}; # 1

---

If you have more than one such variable:

role Auto-Instantiate {
  method AT-KEY (|) is raw {
    my \result = callsame;
    result .= new unless defined result;
    result
  }
}

my Hash[Real,Real] %h{Real} does Auto-Instantiate;