bit_set.rs

struct Helper {
	field1: u64
}

impl Helper {
	fn new (foo: u64) -> Helper {
		Helper { field1: foo }
	}
	
	fn bit_set (&self, bit: u64) -> bool {
		(self.field1 & bit) == bit
	}
	
	fn empty (&self) -> bool {
		!self.bit_set(1)
	}
	
	fn set_a_bit (&self, bit: u64) {
		self.field1 |= bit;
	}
}

fn main () {
	let mut helpera = Helper::new(0);
	
	if helpera.empty() {
		helpera.set_a_bit(2);
	}
}

gistfile1.txt

cremes$ rustc foo2.rs 
foo2.rs:19:3: 19:14 error: cannot assign to immutable field
foo2.rs:19 		self.field1 |= bit;
           		^~~~~~~~~~~
error: aborting due to previous error