Traditional C-style for loops are deprecated

Paul Hudson      @twostraws

This changed outlawed the following syntax in Swift:

for var i = 1; i <= 10; i += 1 {
    print("\(i) green bottles")
}

These are called C-style for loops because they have long been a feature of C-like languages, and conceptually even pre-date C by quite a long way.

Although Swift is (just about!) a C-like language, it has a number of newer, smarter alternatives to the traditional for loop. The result: this construct was deprecated in Swift 2.2 and will be removed "in a future version of Swift."

To replace these old for loops, use one of the many alternatives. For example, the "green bottles" code above could be rewritten to loop over a range, like this:

for i in 1...10 {
    print("\(i) green bottles")
}

Remember, though, that it's a bad idea to create a range where the start is higher than the end: your code will compile, but it will crash at runtime. So, rather than writing this:

for i in 10...1 {
    print("\(i) green bottles")
}

…you should write this instead:

for i in (1...10).reverse() {
    print("\(i) green bottles")
}

Another alternative is just to use regular fast enumeration over an array of items, like this:

var array = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

for number in array {
    print("\(number) green bottles")
}

Although if you want to be technically correct (also known as "the best kind of correct") you would write such a beast like this:

var array = Array(1...10)

for number in array {
    print("\(number) green bottles")
}

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Other changes in Swift 2.2…

• ++ and -- are deprecated
• Comparing tuples
• Tuple splat syntax is deprecated
• More keywords can be used as argument labels
• Variable parameters have been deprecated
• Renamed debug identifiers: line, function, file
• Stringified selectors are deprecated
• Compile-time Swift version checking

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