What is this operator: &=

Question

Can someone explain what is the operator &= for?

I searched, but I got only results with & or =.

Answer 1

It's a shorthand operator which allows you to collapse

a = a & b

into

a &= b

Apart from bitwise operations on integers, &= can be used on boolean values as well, allowing you to collapse

a = a && b

into

a &= b

However, in the case of logical operation, the expanded form is short-circuiting, while the latter collapsed form does not short-circuit.

Example:

let b() be a function that returns a value and also does stuff that affects the program's state

let a be a boolean that is false

if you do

a = a && b()

the short-circuit happens: since a is false there's no need to evaluate b (and the extra computation that might happen inside b() is skipped).

On the other hand, if you do

a &= b()

the short-circuit doesn't happen: b is evaluated in any case, even when a is false (and evaluating b() wouldn't change the logical outcome), thus any extra computation that might happen inside b() does get executed.