ContextError.swift

protocol ContextError : ErrorType {
	mutating func addContext<T>(type: T.Type)
}

protocol Contextualizable {}
extension Contextualizable {
	func addContext(var error: ContextError) -> ContextError {
		error.addContext(self.dynamicType)
		return error
	}
}

struct Error: ContextError {
	var source : String
	let reason : String
	
	init(reason: String, file: String = __FILE__, function: String = __FUNCTION__, line: Int = __LINE__) {
		self.reason = reason
		self.source = "\(file):\(function):\(line)"
	}
	
	mutating func addContext<T>(type: T.Type) {
		source += ":\(type)"
	}
}

struct Parent: Contextualizable {
	func myFunction() throws {
		throw addContext(Error(reason: "An important reason"))
	}
}

do {
	try Parent().myFunction()
} catch {
	print(error)
}