Re: Switch constants

[Dmitry Olshansky]

On 14.11.2010 1:21, 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?

Well, there is fall-through ;) And there still could be goto's.
In essence "case x:" is nothing but a glorified local label.

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

--
Dmitry Olshansky