Searchable.swift

import Foundation

protocol Searchable {
    /// Array of searchable properties converted to strings
    var searchStrings: [String?] { get }
}

extension Searchable {

    func contains(searchText: String) -> Bool {
        let text = searchText.lowercased()
        let searchStrings = self.searchStrings.compactMap { $0 }

        return searchStrings.lazy.filter({ $0.lowercased().contains(text) }).first != nil
    }
}

SearchTableType.swift

import UIKit

/**
 A convenient way to filter your table with a search bar.

Example use:

     extension MyTableViewController: SearchTableType {

        func searchBar(_ searchBar: UISearchBar, textDidChange searchText: String) {
            filterContent(for: searchText, showAllOnEmpty: true)
        }

        func searchBarSearchButtonClicked(_ searchBar: UISearchBar) {
            searchBar.resignFirstResponder()
            tableView.reloadData()
        }
    }

*/
protocol SearchTableType: class, UISearchBarDelegate {
    associatedtype T: Searchable

    var tableView: UITableView! { get }
    var searchBar: UISearchBar! { get }
    var searchableItems: [T] { get }
    var filteredItems: [T] { get set }
}

extension SearchTableType {

    var displayItems: [Searchable] {
        return isFiltering
            ? filteredItems
            : searchableItems
    }

    var isFiltering: Bool {
        return searchBar.isFirstResponder && !searchBarIsEmpty
    }

    var searchBarIsEmpty: Bool {
        return searchBar.text?.isEmpty ?? true
    }

    func filterContent(for searchText: String, showAllOnEmpty: Bool = true) {
        if showAllOnEmpty && searchText.isEmpty {
            filteredItems = searchableItems
        } else {
            filteredItems = searchableItems.filter { $0.contains(searchText: searchText) }
        }
        tableView.reloadData()
    }
}