Switch constants

[Stanislav Blinov]

bearophile wrote:
> In a not-ranged cases body, like in the program below (that doesn't compile), the switch variable is a compile-time constant, so why doesn't the compile see x as constant there?
> 
> 
> template Foo(uint x) {
>     static if (x <= 1)
>         enum Foo = 1;
>     else
>         enum Foo = x * Foo!(x - 1);
> }
> 
> int bar(uint x) {
>     switch (x) {
>         case 0: return Foo!x;
>         case 1: return Foo!x;
>         case 2: return Foo!x;
>         case 3: return Foo!x;
>         case 4: return Foo!x;
>         default: return -1;
>     }
> }
> 
> void main() {
>     assert(bar(4) == 24);
> }
> 
> 
> That code works if I replace lines like:
> case 2: return Foo!x;
> 
> With:
> case 2: return Foo!2;
> 
> But when the code isn't DRY bugs may happen...
> (There are ten different better ways to write that program, but this is not the point).
> 
> Bye,
> bearophile

I would say that while bar may be CTFE'd, it is nevertheless a function 
that can be called at runtime, in which case x may no longer be a 
compile-time constant. So there is little compiler can do except for 
refusing such code.