Random string samples & unicode - Reprise

[dsimcha]

== Quote from bearophile (bearophileHUGS at lycos.com)'s article
> Jonathan M Davis:
> > Well, I don't think that I've ever seen a program that did that sort of thing.
> It's common Python code (and maybe in future it will be common D2 code). In
another answer I have given few examples to Andrei.
> > If your string processing doesn't require random access, then you
> > avoid the problem, but as long as it needs random access, you're pretty much
> > stuck.
> I understand, this is probably the answer I was looking for, thank you :-)
> Bye,
> bearophile

I think what we need here is an AsciiString type.  Such a type would be a thin
wrapper over char[], or maybe immutable(char)[] for added safety.  On construction
it would enforce that the underlying string does not contain any multiple byte
characters.  It would only allow appending of chars, not wchars or dchars.  If you
appended a regular to it, it would throw if the appended string contained any
characters that couldn't be represented in a single byte.  It would be a random
access range of chars with lvalue elements, and would provide a way of documenting
the assumption that you're only working with ASCII, and a mechanism for verifying
this assumption at runtime.