What are "intervals" in swift ranges?

Question

I know there are 3 types of ranges: Range, Strides and Intervals.

var closed:ClosedInterval = 1.2...5.0

var half_open:HalfOpenInterval = 1.2..<5.0

What are intervals in swift? and what is one example of their use?

http://en.wikipedia.org/wiki/Interval_(mathematics)

EDIT: This is what the beta 5 xcode 6 release notes says:

• Intervals over Comparable values, which can efficiently check for containment. Intervals are used for pattern matching in switch statements and by the ~= operator.

Answer 1

As of Swift 3 (with Xcode 8), the Interval types are no more. Now the family of Range<T> types include the functionality of both the former range and interval types, and additionally conform to the new model for collection types and indices.

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In Swift 2.x and older... Ranges are for iterating, and Intervals are for pattern matching.

func testNum(num: Int) {
    let interval: HalfOpenInterval = 0..<10
    let range = 10..<20
    switch num {
    case interval:    // this works
        break
    case range:       // error "does not conform to protocol IntervalType"
        break
    default:
        break
    }
}

A Range type is optimized for generating values that increment through the range, and works with types that can be counted and incremented.

An Interval type is optimized for testing whether a given value lies within the interval. It works with types that don't necessarily need a notion of incrementing, and provides operations like clamping one range to another (e.g. (0..<10).clamp(5..<15) yields 5..<10) that are useful for complex pattern matching.

Because the ..< and ... operators have two forms each--one that returns a Range and one that returns an Interval--type inference automatically uses the right one based on context. So, if you write 0..<10 in a case label of a switch statement, Swift automatically constructs a HalfOpenInterval because a switch statement requires an Interval type.

The ~= operator is a way to do one test on an interval without a switch statement. Writing interval ~= value is equivalent to interval.contains(value).

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It's worth noting that you can find out many of these things by looking at the standard library interface and its comments: write a type name like HalfOpenInterval in a playground, then command-click to jump to its definition.