Examples of DFA

[Richard (Rikki) Andrew Cattermole]

On 24/09/2025 5:54 AM, Walter Bright wrote:
> On 9/23/2025 2:43 AM, Richard (Rikki) Andrew Cattermole wrote:
>> Instead of writing ``@nogc``, we write ``@nogc iff(foo, bar, abc)``.
>>
>>  From there its a simple dependency resolver either during the 
>> compilation of the three functions or on usage.
> 
> It's not so simple when there is recursion in the flow graph.

For @nogc and pure, it is that simple.

Other attributes can't be solved with this solution. They are too 
complex, or effect the calling convention of the function.

I don't have a generalized solution.

>> This is the basis for my solution to a problem Adam has proposed for 
>> PhobosV3, which essentially is the desire to whitelist attributes. Use 
>> ``@localnogc`` & if the function calls are all ``@nogc``, therefore 
>> the function is allowed to be ``@nogc``.
> 
> I am reluctant to try to fix this issue with even more attributes.

If you don't, you're limited to a single compilation.

Which may be fine for a single module, but might not be cross-module.

>> Am I right to assume that the reason you haven't presented this 
>> solution, is because you want attributes to be finalized when bar&abc 
>> complete?
> 
> I showed the solution to illustrate the requirement for iteration and 
> convergence to resolve cycles in the flow graph. A DFA that cannot deal 
> with recursion is just going to leave people frustrated, as the current 
> @nogc inference engine does. 

Indeed. I'd call it an all right example, a better example might be:

```d
void* global;

void thing(T)(scope void* u, T* v) {
	global = v;
	thing(null, u);
}
```

You can't solve for this without applying outputs into inputs.
Therefore no shortcuts.