A Rust array is a fixed-length sequence of values of one type. Its length is known at compile time, unlike a slice’s length, which can be determined at run time. Use an array when the sequence length is fixed; borrow it as a slice when an operation should work with a length determined at run time. section 4.2
The listing initializes 64 zero-valued bytes with `[0u8; 64]`, then borrows the array as `&[u8]`. The slice provides a sequence view without making the array’s fixed length part of the slice type. section 4.2
Length matters when designing interfaces: an array length must be available to the compiler and represented in the type signature. Since Rust 1.51, const generics permit generic arrays with lengths chosen at compile time, not at run time. For work on parts of a sequence, a slice can be split into nonoverlapping subslices, as with `split_at(32)`. section 4.2
