I noticed that all of the number type in Arg is u64, why aren't they usize?

@Donough Liu usize is appropriate for "size of an array or string or similar that fits in memory". It isn't appropriate for arbitrary numeric values.

An arbitrary numeric command-line argument should not have a maximum size that varies by platform.

@Josh Triplett All of the u64 in the Arg is for array size. Changing them to usize doesn't affect a numeric argument's value range. :sweat_smile:

It's pretty internal though.

Ah, sorry, I didn't realize you meant internal to a structure.

Thanks for clarifying.

Then yeah, usize sounds fine.