Casting with As

as works for both lossless and lossy conversions.

When casting from one integer type to another integer type, with the same number of bits, it is a no-op, as in nothing happens. The underlying bits have not changed, merely the lens which these bytes are interpreted changes from that of a u128 to an i128. Unlike From, the true value of the integer is not maintained and the bits are merely interpreted as the destination type's encoding.

#![allow(unused)]
fn main() {
println!("128_u8 `as` i8 becomes {}", 128_u8 as i8);
// 128_u8 `as` i8 becomes -128
}

Rust Reference on Type Casting

Rust Reference on Casting Semantics

https://doc.rust-lang.org/stable/rust-by-example/types/cast.html