Optional values

Optional values can be declared by adding a ? to the end of the type name. This declares that the variable may not have some value, but since this language is strictly typed, all cases must be handled if the value is used somewhere. You can use the none keyword to initialise a variable without a value:

int? myNum = none

However, this will not be directly compatible with the regular type, and so a check must be done first to ensure that the value exists before it can be used.

fn optAddNum(int a, int? b) -> int {
  if b == none {
    return a
  }

  // type of b is now `int` since the none case was handled above
  return a + b
}

However, if the check is not done, an error is thrown:

fn optAddNum(int a, int? b) {
  return a + b // error: none case not handled
}

Since optional values are technically a superset of regular values, you can pass regular values to optionals, but the opposite is not true.

int? num1 = 7 // this is okay
int num2 = none // error: cannot assign none to a non-optional value

fn myFunction(str? arg1, str arg2) {
  // some implementation...
}

myFunction("Hello", "world") // this is okay
myFunction(none, "world") // this is also okay
myFunction("Hello", none) // error: cannot pass none to a non-optional parameter

There are no non-null assertions, so the none case must always be handled.