iOS: Swift code in objective C project

1) Create new *.swift file (in Xcode) or add it by using Finder
2) Add swift bridging empty header if Xcode have not done this before (see 4 below)
3) Implement your Swift class by using @objc attribute:
import UIKit

@objc class Hello: NSObject {
    func sayHello() {
        print("Hi there!")
    }
}
4) Open Build Settings and check those parameters:
    Product Module Name : myproject
    Defines Module : YES
    Embedded Content Contains Swift : YES
    Install Objective-C Compatibility Header : YES
    Objective-C Bridging Header : $(SRCROOT)/Sources/SwiftBridging.h
5) Import header (which is auto generated by Xcode) in your *.m file
    #import "myproject-Swift.h"
6) Clean and rebuild your Xcode project
7) Profit!