from @jazbo, custom tab bar using tags and no duplicate methods (one IBAction, one delegate method)

custom Tab Bar with single IBAction

protocol SectionSelected {
    func sectionSelected(section: SectionType)
}
class TestClass {
    
    weak var tabBarDelegate: SectionSelected?
    
    var sectionType: SectionType? {
        didSet {
            sectionSelected()
        }
    }
    
    func buttonPressed(sender: UIButton) {
        switch sender.tag {
        case 1:
            self.sectionType = SectionType.One
        case 2:
            self.sectionType = SectionType.Two
        case 3:
            self.sectionType = SectionType.Three
        default: break
        }
    }
    
    
    // MARK: - Helper Methods
    func sectionSelected() {
        guard let tabBarDelegate = tabBarDelegate, sectionType = sectionType else {
            return
        }
        tabBarDelegate.sectionSelected(sectionType)
    }
}

class Two: SectionSelected {
    func sectionSelected(section: SectionType) {
        // use selected section here
    }
}