Is there a more elegant way to do this in D?

[Paul Backus]

On Thursday, 8 April 2021 at 22:27:38 UTC, Alain De Vos wrote:
> So which concrete types do you give for the two auto's.

The first `auto` is the return type of `to!(ubyte[])`--so, it's 
`ubyte[]`.

The second `auto` is the return type of `map`. If you look at the 
documentation [2], you'll see that it doesn't give a concrete 
type for the return value; it just says that `map` returns "an 
input range." That's because the concrete type is a so-called 
"Voldemort type" [1]--a type whose name is private to the 
function, and can't be used externally.

Why use such a type? Because it gives the authors of `map` the 
freedom to change the concrete type without breaking code that 
uses `map`, as long as the type they change it to still supports 
the input range interface.

[1] https://wiki.dlang.org/Voldemort_types
[2] 
https://phobos.dpldocs.info/std.algorithm.iteration.map.map.html