Is it expected that too big a bit-shift will be undefined in Rust?

Question

When running this code:

#![allow(exceeding_bitshifts)]

fn main() {
    const NUMBER: u64 = 0b_10101010;

    fn print_shift(i: u32) {
        println!("{:b}", NUMBER >> i);
    }

    print_shift(65);
    println!("{:b}", NUMBER >> 65);
}

You see that shifting the bits of a number with a value longer than the bit length causes a different behavior when executed at compile time or at run time.

Is this normal behavior? Is this documented somewhere? This is not on the list of documented behavior undefined .

Answer 1

No, this is not , but it is not undefined behavior . This is a “simple” mistake .

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