Constant items - The Rust Reference

# Constant items

A constant item is a named constant value which is not associated with a specific memory location in the program. Constants are essentially inlined wherever they are used, meaning that they are copied directly into the relevant context when used. References to the same constant are not necessarily guaranteed to refer to the same memory address.

Constant values must not have destructors, and otherwise permit most forms of data. Constants may refer to the address of other constants, in which case the address will have elided lifetimes where applicable, otherwise – in most cases – defaulting to the `static` lifetime. (See below on static lifetime elision.) The compiler is, however, still at liberty to translate the constant many times, so the address referred to may not be stable.

Constants must be explicitly typed. The type may be any type that doesn't implement `Drop` and has a `'static` lifetime: any references it contains must have `'static` lifetimes.

    # #![allow(unused_variables)]
    #fn main() {
    const BIT1: u32 = 1 << 0;
    const BIT2: u32 = 1 << 1;

    const BITS: [u32; 2] = [BIT1, BIT2];
    const STRING: &'static str = "bitstring";

    struct BitsNStrings<'a> {
        mybits: [u32; 2],
        mystring: &'a str,
    }

    const BITS_N_STRINGS: BitsNStrings<'static> = BitsNStrings {
        mybits: BITS,
        mystring: STRING,
    };
    #}