I decided to write my own N-D array implementation using generics for the number of dimensions:

pub struct ArrayNd<const N: usize, T> {
    shape: [usize; N],
    data: Vec<T>,
}

I wrote a maze generation algorithm and realized it cleanly generalizes to N dimensions. Examples:

That's pretty cool! Let's let users specify these dimensions from the CLI, I thought.

I added clap with a Vec<usize> param and then it hit me. Since my type is "generic" and compiles to actual constant-size instances, I will not be able to do this.

A solution would be to remove the generic N and rewrite the library to something like:

pub struct ArrayNd<T> {
    shape: Vec<usize>,
    data: Vec<T>,
}

That is a lot of work, loses compile-time checks, and is not even zero-cost.

I got an idea, why doesn't Rust provide a feature for "unspecified" or "run-time" generics? All unspecified parameters could be Boxed and you could only have a single compiled type for "run-time" use cases. (Of course, there could also be "half-specified" types.)

I would like to hear your opinions:

• Would "unspecified generics" be possible?
• Would "unspecified generics" be feasible?
• Are there other options that I'm missing?
• Have you encountered a similar situation?
• Have you ever felt a little disillusioned about generics?

Thanks for reading and replies.

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