switch statement with variable branches

[Yuxuan Shui via Digitalmars-d-learn]

On Thursday, 19 January 2017 at 02:00:10 UTC, Ali Çehreli wrote:
> On 01/18/2017 05:22 PM, Yuxuan Shui wrote:
>> Somehow I can't use ubyte variables behind 'case', but ulong 
>> works fine.
>> Why is that?
>>
>
> case expressions must be constants:
>
>   "The case expressions must all evaluate to a constant value or
>    array, or a runtime initialized const or immutable variable 
> of
>    integral type."
>
>   https://dlang.org/spec/statement.html#SwitchStatement
>
> The fact that it compiles for ulong looks like a bug to me. It 
> compiles probably because switch is most likely implemented in 
> terms of a chained if-else-if statements by the compiler and it 
> just works because there is no explicit check whether they are 
> constant or not.
>
> Ali

If you try:

void main() {
     alias TestType = ulong; // won't compile if = ubyte
     import std.stdio;
     TestType a,b,c;
     readf("%s %s %s ", &a, &b, &c);
     final switch(c){
         case a: writeln("a");break;
         case b: writeln("b");break;
         default: assert(false);
     }
}

Then the error message:

test.d(7): Error: case variables not allowed in final switch 
statements
test.d(8): Error: case variables not allowed in final switch 
statements

Makes it looks like that "case variable" is an intended feature.