String Interpolation

[Arafel]

On 25/10/23 8:49, Walter Bright wrote:
> Thank you. The trouble is with the mixin. It can't be dispensed with.

Well, I know you want to make mixins clearly identifiable, but I would 
suggest some easy sintax for string mixins generated by a template.

For instance, using `!!` (I think it's an unused token):

```d
foo!!(a, 42)
```

would be literally just another way of writing:

```d
mixin(foo!(a,42))
```

and thus anybody could implement:

```d
i!!"Helo ${name}"
```

as a library solution, or even use the existing ones.

You could create mixins that are tighly coupled to the called function, 
or generic ones... it would be the most flexible solution.