Solution to "statement is not reachable" depending on template variables?

[Johan Engelen via Digitalmars-d-learn]

On Friday, 1 April 2016 at 01:21:32 UTC, Walter Bright wrote:
> On 3/16/2016 4:18 AM, Johan Engelen wrote:
>>    I've found discussions, but not an actual "recommended" 
>> solution for the
>> problem of "statement is not reachable" warnings in templates 
>> with early
>> returns, e.g.:
>> ```
>> bool nobool(T...)() {
>>      foreach (i, U; T) {
>>          static if (is(U == bool)) {
>>              return false;
>>          }
>>      }
>>      return true;  // emits "Warning: statement is not 
>> reachable"
>> }
>
>
> bool nobool(T...)() {
>      bool result = true;
>      foreach (i, U; T) {
>          static if (is(U == bool)) {
>              result = false;
>              break;
>          }
>          else
>          {
>              ...
>          }
>      }
>      return result;  // emits "Warning: statement is not 
> reachable"
> }

As you can see from my first post, that is the solution I used 
first  (without the "break;" addition), but it works until...

> Note that the optimizer will remove the dead loads.

... until someone adds a (imho useful) diagnostic of dead 
stores/loads. :-)
In that case, I guess inverting all bools and then inverting the 
return value at the end will work (using default initialization 
of result); but this is not possible in a slightly more 
complicated case with non-bool return types.

In another piece of code, the return type is a struct with an 
immutable member. That's when I gave up on working around the 
warning and just disabled it.
Simplified, something like this:

struct IMM {
     immutable bool result;
}
IMM immut(T...)() {
     IMM retval = IMM(true);
     foreach (i, U; T) {
         static if (is(U == bool)) {
             retval = IMM(false);  //  "Error: cannot modify 
struct retval IMM with immutable member".
         }
     }
     return retval;
}