Notice how you'd need to generate the DS for every type you'd like to use it with, which is not the case with built in mutable maps and slices.
To make them type-safe, you need to generate them for every type you use. While this is technically possible, it does make the language quite hostile towards functional programming. With generics, this is rectified but the problem with non-composable multi-return-value functions still remains
Lets take `map` for example. Before generics, you would have to reimplement map for every type combination. Each implementation would be done with a for loop. Now, while I'm willing to look over having one `map` implementation being done in imperative code and then everything else using that, I'm not exactly comfortable calling reimplementing map with imperative code for every type combination functional programming.
