It's basically Hindley-Milner.

[Elfstone]

On Friday, 24 March 2023 at 09:44:28 UTC, FeepingCreature wrote:

> If we insert the missing step, what the compiler should do is: 
> "Ah, `B` is a 'trivial alias' (like `using` in C++), so I can 
> *syntactically substitute* it with its content", and create the 
> new expression `B!int = B!T`. Then it can resolve this by 
> noting that *the concrete type* `B!int` is an instance of `B` 
> with the type `int`, and thus gain the new expression `T = 
> int`, which solves the algebraic system.

That alone will be a huge improvement.

There's no need to resolve all cases. DIP1023 should not try to 
do that, if it's ever picked up.

```C++
template <typename T>
using Identity = int;

template <typename T>
void bar(Identity<T> id) {

}

int main() {
	bar(Identity<int>());
}
```

C++ doesn't automatically resolve this either, and I bet no one 
will ask it to.

When you think about it: for now, D allows writing template alias 
paramters, but AFAIK they will match absolutely **nothing**! 
Nothing you pass will ever be accepted.