DateUtils.swift

extension DateFormatter {
	/*
		DateFormatters are notoriously slow to create, so it's best to share them. 
		However, they're not thread safe, so this returns one DateFormatter per thread.
	*/
	static var shared : DateFormatter {
		let key = "com.relium.swift.DateFormatter" 
		if let f1 = Thread.current.threadDictionary[key] as? DateFormatter {
			return f1
		}
		else {
			let f2 = DateFormatter()
			Thread.current.threadDictionary[key] = f2
			return f2
		}
	}
	
	static let using12hClockFormat : Bool = {
		let formatter = DateFormatter()
		formatter.locale = Locale.current
		formatter.dateStyle = .none
		formatter.timeStyle = .short

		let dateString = formatter.string(from: Date())
		let amRange = dateString.range(of: formatter.amSymbol)
		let pmRange = dateString.range(of: formatter.pmSymbol)

		return !(pmRange == nil && amRange == nil)
	}()
}

// TODO: Use new @ThreadSpecific when it works???
// DateFormatters are notoriously slow to create, so it's best to share them. 
// However, they're not thread safe, so this returns one per thread.
extension ISO8601DateFormatter {
	static public var shared : ISO8601DateFormatter {
		get {
			let threadDict = Thread.current.threadDictionary
			let key = "com.relium.swift.isoDateFormatter"
			 
			if let formatter = threadDict[key] as? ISO8601DateFormatter {
				return formatter
			}
			else {
				let newFormatter = ISO8601DateFormatter()
				threadDict[key] = newFormatter
				return newFormatter
			}
		}
	}
}