Swift Xcode extension snippet for getting array of strings from lines.

GetLinesStrings.swift

//
//  GetLinesStrings.swift
//
//  Created by Dominik Bucher on 22/10/2017.
//  Copyright © 2017 Dominik Bucher. All rights reserved.
//
    
    /// This method should be universal and implemented right from Apple.
    ///  gets specified text from line indexes
    ///
    /// - Parameters:
    ///   - buffer: buffer to work with(usually the same instance as in all other functions)
    /// - Returns: returns array of texts on specific lines
    class func getSelectedLinesText(withBuffer buffer: XCSourceTextBuffer) throws -> [String]{

        guard let selectedRange = buffer.selections as? [XCSourceTextRange],
              let firstRange = selectedRange.first
        else { throw NSError() } // You can handle the completion handler here, something like no selection or something like that...

        let indexes = Array(firstRange.start.line...firstRange.end.line)

        return indexes.map({ buffer.lines[$0] as? String }).flatMap({$0})
    }
    
    
    // MARK: - Usage: 
    
    class SourceEditorCommand: NSObject, XCSourceEditorCommand {
    
     func perform(with invocation: XCSourceEditorCommandInvocation, completionHandler: @escaping (Error?) -> Void ) -> Void {

        do {

            let selectedLines = try getSelectedLinesText(withBuffer: invocation.buffer)
            // Prints array of selected lines, not limited by UTI or anything... Cool thing about the Xcode extensions is
            // that you can use them in any other language like Python or Ruby 👌🏻.
            // Print isn't handled in Xcode extensions too well,
            // see this: https://stackoverflow.com/questions/41948124/print-not-working-in-swift-3-extensions
            // for further disambiguation.
            print(selectedLines)
        }
        catch let err { completionHandler(err) }
        completionHandler(nil)
    }
    

Maybe it would be nice to add this as extension to XCSourceEditorCommand protocol to have it straight build-in and ready to go... But I don't really like real implementations in protocol extensions... So I will think about another idea...