Thin UTF8 string wrapper

[Joseph Rushton Wakeling]

Hello folks,

I have a use-case that involves wanting to create a thin struct 
wrapper of underlying string data (the idea is to have a type 
that guarantees that the string has certain desirable properties).

The string is required to be valid UTF-8.  The question is what 
the most useful API is to expose from the wrapper: a sliceable 
random-access range?  A getter plus `alias this` to just treat it 
like a normal string from the reader's point of view?

One factor that I'm not sure how to address w.r.t. a full range 
API is how to handle iterating over elements: presumably they 
should be iterated over as `dchar`, but how to implement a 
`front` given that `std.encoding` gives no way to decode the 
initial element of the string that doesn't also pop it off the 
front?

I'm also slightly disturbed to see that `std.encoding.codePoints` 
requires `immutable(char)[]` input: surely it should operate on 
any range of `char`?

I'm inclining towards the "getter + `alias this`" approach, but I 
thought I'd throw the problem out here to see if anyone has any 
good experience and/or advice.

Thanks in advance for any thoughts!

All the best,

      -- Joe