Discussion Thread: DIP 1042--ProtoObject--Community Review Round 1

[Timon Gehr]

On 1/15/22 13:02, Elronnd wrote:
> 
>> You can't, as any `pure` function can just call toHash.
> 
> Not sure what you mean.  I propose to pretend to the compiler that 
> Object's constructor is pure, even though it is not (it must access 
> global state to calculate a hash for the object).
> 
> If the issue is that pure functions can call toHash and its output is 
> 'non-deterministic' then ... I really don't have any more to say.  
> toHash always returns the same result given the same input.

I said toHash can't be pure, you suggested to make the constructor cheat 
so toHash can be pure. I said that does not work. I also don't have much 
more to say, but maybe I can say the same thing again.

The problem is this:

```d
hash_t stronglyPure()@safe pure nothrow;
```

This returns an integer (or perhaps it throws an error). It should 
always be the same integer as it is a `pure` function without any 
parameters. However, it will return a different result on each 
invocation if I implement it like this:

```d
hash_t stronglyPure()@safe pure nothrow{
     return new Object().toHash();
}
```

I really don't care if the constructor is cheating or toHash. The point 
is, you can't cheat.