Are "&&" and "," the same in Swift?

Question

As the title says, I just came across a case where if && (AND) and , give the same result in Swift. I tested the code below:

let a = 5
let b = 6

if a<6, b>0 {
    print("should be true")
}

if a<6, b<0 {
    print("should be false")
}

if a>6, b>0 {
    print("should be false")
}

if a>6, b<0 {
    print("should be false")
}

It only logs:

should be true

So, the behavior of , is just like &&, am I correct?

Answer 1

They can be used in similar situations but that does not mean they are exactly the same.

Consider:

if (a && b) || c

you cannot write

if (a, b) || c

even a && b || c is different from a, b || c.

if a, b is something like

if a {
   if b {
      ...
   }
}

Both expressions have to be evaluated to true but they are still two separate expressions. We shouldn't imagine && there.

Why do we need the , operator?

The operator is needed to combine optional binding with boolean conditions, e.g.

if let a = a, a.isValid() {

becuase && wouldn't help us in such situations.

Answer 2

They're different in that a comma will take the lowest precedence possible. i.e everything else will be executed before the commas are checked.

// (true || false) && false
if true || false, false {
    print("I will never be executed")
}

// true || (false && false)
if true || false && false {
    print("I am always executed")
}