Constant MAX_ELEMENTS 

pub const MAX_ELEMENTS: usize = _; // 4_294_967_296usize

The most elements one value may hold.

Set by what a machine can plausibly hold rather than by J or APL, both of which put no limit in the language: 2^32 elements is 32 GB of doubles, past any real working set and far short of a request that would take the process down.