Marcus Leon Marcus Leon - 18 days ago 7
iOS Question

Swift if statement - multiple conditions separated by commas?

Looking at a Swift example:

if let sourceViewController = sender.sourceViewController as? MealViewController, meal = sourceViewController.meal {
...
}


The doc states:


... the code assigns that view controller to the local
constant sourceViewController, and checks to see if the meal property
on sourceViewController is nil.


Question: Does Swift let you have multiple conditions in your if statement when separated by commas (as in this example with the comma after
MealViewController
)?

Haven't seen this in the docs.

Answer

Yes when you write

if let a = optA, let b = optB, let c = optC {

}

Swift will execute the body of the IF only if all the assignments are properly completed.

More

Another feature of the technique is that the assignments are done in order.

So only if a value is properly assigned to a, Swift tries to assign a value to b. And so on.

This allows you to use the previous defined variable/constant like this

if let a = optA, let b = a.optB {

}

In this case (in second assignment) we are safely using a because we know that if that code is executed, then a has been populated with a valid value.