Multiple variable assignment in Swift

Question

How do I assign multiple variables in one line using Swift?

    var blah = 0
    var blah2 = 2

    blah = blah2 = 3  // Doesn't work???

Answer 1

You don't.

This is a language feature to prevent the standard unwanted side-effect of assignment returning a value, as described in the Swift book:

Unlike the assignment operator in C and Objective-C, the assignment operator in Swift does not itself return a value. The following statement is not valid:

   if x = y {
       // this is not valid, because x = y does not return a value
   }

This feature prevents the assignment operator (=) from being used by accident when the equal to operator (==) is actually intended. By making if x = y invalid, Swift helps you to avoid these kinds of errors in your code.

So, this helps prevent this extremely common error. While this kind of mistake can be mitigated for in other languages—for example, by using Yoda conditions—the Swift designers apparently decided that it was better to make certain at the language level that you couldn't shoot yourself in the foot. But it does mean that you can't use:

blah = blah2 = 3

If you're desperate to do the assignment on one line, you could use tuple syntax, but you'd still have to specifically assign each value:

(blah, blah2) = (3, 3)

...and I wouldn't recommend it. While it may feel inconvenient at first, just typing the whole thing out is the best way to go, in my opinion:

blah = 3
blah2 = 3