Using a char value >= 128

[Ernesto Castellotti]

On Sunday, 27 October 2019 at 12:44:05 UTC, Per Nordlöw wrote:
> In which circumstances can a `char` be initialized a non-7-bit 
> value (>= 128)? Is it possible only in non- at safe code?
>
> And, if so, what will be the result of casting such a value to 
> `dchar`? Will that result in an exception or will it interpret 
> the `char` using a 8-bit character encoding?
>
> I'm asking because I'm pondering about how to specialize the 
> non-7-bit `needle`-case of the following array-overload of 
> `startsWith` when `T` is `char`:
>
> bool startsWith(T)(scope const(T)[] haystack,
>                    scope const T needle)
> {
>     static if (is(T : char)) { assert(needle < 128); } // TODO 
> convert needle to `char[]` and call itself
>     if (haystack.length >= 1)
>     {
>         return haystack[0] == needle;
>     }
>     return false;
> }

char in D is always unsigned, it is not implementation-specific.
Therefore it can take values ​​up to (2^8)−1, If you want a 
signed 8 byte type you can use ubyte, which obviously can take up 
from -(2^7) to (2^7)-1