A new implementation of `flatMap(f:)` added to `SequenceType` in Swift 2.0.

RageMap.swift

extension SequenceType {
    /// Return an `Array` containing the non-nil results of mapping
    /// `transform` over `self`.
    ///
    /// - Complexity: O(*M* + *N*), where *M* is the length of `self`
    ///   and *N* is the length of the result.
    public func flatMap<T>(@noescape transform: (Self.Generator.Element) -> T?) -> [T]
}