assert(false)

[monarch_dodra]

On Thursday, 20 June 2013 at 23:36:35 UTC, Joseph Rushton 
Wakeling wrote:
> On 06/20/2013 11:36 PM, Jonathan M Davis wrote:
>>> ... one is necessary as it's in a function that is supposed 
>>> to return a
>>> value.
>> 
>> I don't think that that's supposed to be necessary. The only 
>> reason that that should happen is if the compiler can 
>> deterimine that the execution can definitely reach the end of 
>> the function.
>
> It's in diceImpl:
>
>     private size_t diceImpl(Rng, Range)(ref Rng rng, Range 
> proportions)
>     if (isForwardRange!Range && isNumeric!(ElementType!Range) 
> && isForwardRange!Rng)
>     {
>         double sum = reduce!("(assert(b >= 0), a + b)")(0.0, 
> proportions.save);
>         enforce(sum > 0, "Proportions in a dice cannot sum to 
> zero");
>         immutable point = uniform(0.0, sum, rng);
>         assert(point < sum);
>         auto mass = 0.0;
>
>         size_t i = 0;
>         foreach (e; proportions)
>         {
>             mass += e;
>             if (point < mass) return i;
>             i++;
>         }
>         // this point should not be reached
>         assert(false);
>     }
>
> Obviously one can see logically that this assert will never be 
> reached, but I
> don't think there's anything the compiler can pick up on to be 
> certain.

Reading that code, it's not immediately obvious to me: The assert 
makes it self documenting.

In any case, this goes back to what I first said: If you remove 
that assert, the compiler will complain that not all paths return.