I had the same problem a few months ago. It's the same with Algebraic, too bad.

alias TypeTuple!(int, string, double, char) Universe;
alias Algebraic!Universe Var;
Var[string] test;

test["abc"] = 3; // fails, also with range violation.

test["abc"] = Var(3); // the same. even wrapped in an Algebraic/Variant call, you cannot initialize it.

test = ["abc":3]; // Error: cannot implicitly convert expression (["abc":1]) of type int[string] to VariantN!(maxSize,int,string,double,char)[string]

test = ["abc":Var(3)]; // Error: cannot implicitly convert expression (["abc":opCall(3)]) of type VariantN!(maxSize)[string] to...

(note the weird expression, but with a correct type.)

In the end, I had to use a two-level hack:

Variant[] vars;
int[char[]][int] indices;

vars ~= "Jan";
indices[0]["Month"] = vars.length-1;

or something like this. Sad, but true...

  Philippe