string types: const(char)[] and cstring

[Walter Bright]

Under the new const/invariant/final regime, what are strings going to be 
? Experience with other languages suggest that strings should be 
immutable. To express an array of const chars, one would write:

	const(char)[]

but while that's clear, it doesn't just flow off the keyboard. Strings 
are so common this needs an alias, so:

	alias const(char)[] cstring;

Why cstring? Because 'string' appears as both a module name and a common 
variable name. cstring also implies wstring for wchar strings, and 
dstring for dchars.

String literals, on the other hand, will be invariant (which means they 
can be stuffed into read-only memory). So,
	typeof("abc")
will be:
	invariant(char)[3]

Invariants can be implicitly cast to const.

In my playing around with source code, using cstring's seems to work out 
rather nicely.

So, why not alias cstring to invariant(char)[] ? That way strings really 
would be immutable. The reason is that mutables cannot be implicitly 
cast to invariant, meaning that there'd be a lot of casts in the code. 
Casts are a sledgehammer, and a coding style that requires too many 
casts is a bad coding style.