Swift `for-in` loop Range and ClosedRange errors

Question

I'm attempting to write simple Swift for loops like so:

for i in [0...10] {
    // ...
}

for i in [0..<10] {
    // ...
}

These for-in loops over a range are important due to the absence of classic C-style for loops in Swift. I am attempting to enumerate over any array of Ints built via Swift's ... and ..< syntax.

Note that if I construct an array of Ints "manually" rather than use [...] or [..<], it works fine:

for i in [0, 1, 2, 3, 4, 5] {
    // this works fine 
}

But the [0..<5] loops produce errors basically any time I try to use the value i:

let _ = i + 1

Here are the errors I get:

- Binary operator `'+'` cannot be applied to operands of type `'ClosedRange<Int>'` and `'Int'`  

- Binary operator `'+'` cannot be applied to operands of type `'Range<Int>'` and `'Int'  `

I have also tried this:

let _ = String(i)

And I get:

Ambiguous reference to initializer `'init(_:)'`

Why are these simple for-in loops not working?

Why are the errors referencing Range and ClosedRange? I am expecting an Int.

Answer 1

Swift ranges are written as 0...10, not [0...10].

---

[0...10] creates a single-item array. The first item in the array is a 0...10 range.

Using for i in [0...10] thus iterates over that single-item array, not the range itself. The iterated value i will be of type Range or ClosedRange.

To iterate over each Int in the range, as you expect to be doing, use the range 0...10 without the brackets:

for i in 0...10 {
    // ...
}

for i in 0..<10 {
    // ...
}

---

https://docs.swift.org/swift-book/LanguageGuide/ControlFlow.html

You can also use for-in loops with numeric ranges. This example prints the first few entries in a five-times table:

for index in 1...5 {
    print("\(index) times 5 is \(index * 5)")
}

The sequence being iterated over is a range of numbers from 1 to 5, inclusive, as indicated by the use of the closed range operator (...).