Appending static arrays

[Nordlöw via Digitalmars-d-learn]

On Monday, 17 July 2017 at 17:38:23 UTC, Nordlöw wrote:
> I'm want to define a specialization of `append()` that takes 
> only static arrays as inputs and returns a static array being 
> the sum of the lengths of the inputs.
>
> Have anybody already implemented this?
>
> If not, I'm specifically interested in how to most conveniently 
> infer the length (as an enum) of the returned static array from 
> the `.length`s of inputs (which of course must be enum-values 
> too).

I just realized that I can use `std.meta.staticMap` to get the 
lengths but I still need to reduce them and there is no variant 
of `reduce` in `std.meta`. Why? Hasn't it been written yet?

I know I can always write yet another recursive CT-function, say 
`SumOfLengths`, but I thought I'd try to reuse `std.meta` this 
time. :)