[Pitch] Valued break

[Danny]

Sorry, I didn't see this thread before I chimed in on Last expression as return value, and then again. As with the "then pitch", you're on the right track, but as with guard statements there, you're considering problems that actually don't have the possibility of being problems.

@SlugFiller

Note that the label is a must:

let value = if condition {
  // Am I trying to return 3 from the `if`,
  // Or break out of a label called `3:`?
  // This will always be interpreted as the latter,
  // and cause an error if no such label exists
  break 3
}
else {
  break 4
}

1. Numbers are not valid labels.
2. There is no ambiguity because the break has to return the value of the expression, and expressions can't exit outer scope*. This is true even in the probably-never-necessary situation of assigning to a Void variable.

label: do {
  let voidValue = if condition {
    let label = ()
    break label // Would return `()` either way, but has to mean the variable because it's all that's available to an expression.
  } else {
    ()
  }
}

* From today's Swift:

let value: Void = {
  label: do {
    if true { break label } else { } // Compiles
    return if true { () } else { () } // Compiles
    return if true {
      break label // Cannot 'break' in 'if' when used as expression
    } else {
      return // Cannot 'return' in 'if' when used as expression
    }
  }
} ()

---

As a precedent, there's no problem in current Swift with returning variables with the same names as labels.

The following compiles, but if you try putting

break label

before the return in the if or else statement, you'll get

Missing return in closure expected to return 'Int'.

let value = {
  label: do {
    if condition {
      let label = 3
      return label
    } else {
      return 4
    }
  }
} ()