struct PartialRangeUpTo A partial half-open interval up to, but not including, an upper bound. Inheritance RangeExpression You create PartialRangeUpTo instances by using the prefix half-open range operator (prefix ..<). let upToFive = ..<5.0 You can use a PartialRangeUpTo instance to quickly check if a value is contained in a particular range of values. For example: upToFive.contains(3.14) // true upToFive.contains(6.28) // false upToFive.contains(5.0) // false You can use a PartialRangeUpTo instance of a collection's indices to represent the range from the start of the collection up to, but not including, the partial range's upper bound. let numbers = [10, 20, 30, 40, 50, 60, 70] print(numbers[..<3]) // Prints "[10, 20, 30]" Initializers init init(_:) Required Declaration @inlinable public init(_ upperBound: Bound) Instance Variables let upperBound Required Declaration let upperBound: Bound Instance Methods func contains(_ element: Bound) -> Bool Required Returns a Boolean value indicating whether the given element is contained within the range expression. Parameter element: The element to check for containment. Declaration public func contains(_ element: Bound) -> Bool func relative(to collection: C) -> Range<Bound> Required Returns the range of indices described by this range expression within the given collection. You can use the relative(to:) method to convert a range expression, which could be missing one or both of its endpoints, into a concrete range that is bounded on both sides. The following example uses this method to convert a partial range up to 4 into a half-open range, using an array instance to add the range's lower bound. let numbers = [10, 20, 30, 40, 50, 60, 70] let upToFour = ..<4 let r1 = upToFour.relative(to: numbers) // r1 == 0..<4 The r1 range is bounded on the lower end by 0 because that is the starting index of the numbers array. When the collection passed to relative(to:) starts with a different index, that index is used as the lower bound instead. The next example creates a slice of numbers starting at index 2, and then uses the slice with relative(to:) to convert upToFour to a concrete range. let numbersSuffix = numbers[2...] // numbersSuffix == [30, 40, 50, 60, 70] let r2 = upToFour.relative(to: numbersSuffix) // r2 == 2..<4 Use this method only if you need the concrete range it produces. To access a slice of a collection using a range expression, use the collection's generic subscript that uses a range expression as its parameter. let numbersPrefix = numbers[upToFour] // numbersPrefix == [10, 20, 30, 40] Parameter collection: The collection to evaluate this range expression in relation to. Declaration public func relative<C>(to collection: C) -> Range<Bound> where Bound == C.Index, C: Collection Type Methods func ~=(pattern: Self, value: Self.Bound) -> Bool Required Declaration @inlinable public static func ~=(pattern: Self, value: Self.Bound) -> Bool