Swift if conditional: Is 'comma' like 'AND'? [duplicate]

Question

We already know multiple optional bindings can be used in a single if/guard statement by separating them with commas, but not with && e.g.

// Works as expected
if let a = someOpt, b = someOtherOpt {
}
// Crashes
if let a = someOpt && b = someOtherOpt {
}

Playing around with playgrounds, the comma-style format also seems to work for boolean conditions though I can't find this mentioned anywhere. e.g.

if 1 == 1, 2 == 2 {
}
// Seems to be the same as
if 1 == 1 && 2 == 2 {
}

Is this an accepted method for evaluating multiple boolean conditions, and is the behaviour of , identical to that of && or are they technically different?

Answer 1

Actually the result is not the same. Say that you have 2 statements in an if and && between them. If in the first one you create a let using optional binding, you won't be able to see it in the second statement. Instead, using a comma, you will.

Comma example:

if let cell = tableView.cellForRow(at: IndexPath(row: n, section: 0)), cell.isSelected {
    //Everything ok
}

&& Example:

if let cell = tableView.cellForRow(at: IndexPath(row: n, section: 0)) && cell.isSelected {
    //ERROR: Use of unresolved identifier 'cell'              
}

Hope this helps.

Answer 2

In Swift 3, the where keyword in condition clauses were replaced by a comma instead.

So a statement like if 1 == 1, 2 == 2 {} is saying "if 1 equals 1 where 2 equals 2..."

It's probably easiest to read a conditional statement with an && instead of a ,, but the results are the same.

You can read more about the details of the change in Swift 3 in the Swift Evolution proposal: https://github.com/apple/swift-evolution/blob/master/proposals/0099-conditionclauses.md