//
//  NSAttributedStringExtensions.swift
//  ACKategories
//
//  Created by Josef Dolezal on 04/02/2018.
//  Copyright © 2018 Josef Dolezal. All rights reserved.
//

import Foundation

public extension NSAttributedString {
    func byAppending(_ other: NSAttributedString) -> NSAttributedString {
        let result = NSMutableAttributedString()

        result.append(self)
        result.append(other)

        return result
    }

    public static func +(_ lhs: NSAttributedString, _ rhs: NSAttributedString) -> NSAttributedString {
        return lhs.byAppending(rhs)
    }
}

//
//  NSAttributedStringExtensions.swift
//  ACKategories
//
//  Created by Josef Dolezal on 04/02/2018.
//  Copyright © 2018 Josef Dolezal. All rights reserved.
//

import Foundation

precedencegroup ConcatenationGroup {
    associativity: left
    higherThan: AssignmentPrecedence
}

infix operator ++: ConcatenationGroup

public func ++(_ lhs: NSAttributedString, _ rhs: NSAttributedString) -> NSAttributedString {
    return lhs.byAppending(rhs)
}

public extension NSAttributedString {
    func byAppending(_ other: NSAttributedString) -> NSAttributedString {
        let result = NSMutableAttributedString()

        result.append(self)
        result.append(other)

        return result
    }
}

--- 
+++ 
@@ -8,17 +8,6 @@
 
 import Foundation
 
-precedencegroup ConcatenationGroup {
-    associativity: left
-    higherThan: AssignmentPrecedence
-}
-
-infix operator ++: ConcatenationGroup
-
-public func ++(_ lhs: NSAttributedString, _ rhs: NSAttributedString) -> NSAttributedString {
-    return lhs.byAppending(rhs)
-}
-
 public extension NSAttributedString {
     func byAppending(_ other: NSAttributedString) -> NSAttributedString {
         let result = NSMutableAttributedString()
@@ -28,4 +17,8 @@
 
         return result
     }
+
+    public static func +(_ lhs: NSAttributedString, _ rhs: NSAttributedString) -> NSAttributedString {
+        return lhs.byAppending(rhs)
+    }
 }
Use standard '+' for string concatenating
