[local closure](http://ankitthakur.github.io/blog/swift/scope/2016/02/08/localScope.html)
// global closures
public func local(closure: () -> ())
public func localAutoreleasePool(closure: () -> ())

global variables
public var GlobalMainQueue: dispatch_queue_t { get }
public var GlobalUserInteractiveQueue: dispatch_queue_t { get }
public var GlobalUserInitiatedQueue: dispatch_queue_t { get }
public var GlobalUtilityQueue: dispatch_queue_t { get }
public var GlobalBackgroundQueue: dispatch_queue_t { get }

// public tuple for color components
public typealias ColorComponents = (red: CGFloat, green: CGFloat, blue: CGFloat, alpha: CGFloat)

// global functions
public func degreesToRadians(degrees: CGFloat) -> CGFloat
public func radiansToDegrees(radians: CGFloat) -> CGFloat