Deduplicating Template Parameter List of std.variant.Algebraic

[Nordlöw via Digitalmars-d-learn]

On Thursday, 24 September 2015 at 20:20:42 UTC, Nordlöw wrote:
> I just noticed that Algebraic doesn't deduplicate its types 
> before construction because this compiles:
>
>     import std.variant : Algebraic;
>     auto x = Algebraic!(int, int)(5);
>
> Is this really sane?

How can a template parameter list be deduplicated or sorted?