Remove variable string assignment from public interface

It's unclear how to write assignments that work on all String things, even on let Var(...), without compile ambiguity

Author: codeface-io

Code/Public/Variable/Variable+String.swift

@@ -1,12 +1,5 @@
 // MARK: - Concatenating
 
-infix operator +=: AssignmentPrecedence
-
-public func +=<S1: StringValue, S2: StringValue>(str1: inout S1, str2: S2)
-{
-    str1.string = str1.string + str2.string
-}
-
 infix operator +: AdditionPrecedence
 
 public func +<S1: StringValue, S2: StringValue>(str1: S1, str2: S2) -> String

README.md

@@ -22,7 +22,7 @@ SwiftObserver is just about 1200 lines of production code, but it also approache
     * [Introduction](#introduction)
 * [Memory Management](#memory-management)
 * [Variables](#variables)
-    * [Set Variable Values](#set-variable-values)
+    * [Use Variable Values](#use-variable-values)
     * [Observe Variables](#observe-variables) 
     * [Variables are Codable](#variables-are-codable)
 * [Mappings](#mappings)
@@ -177,7 +177,7 @@ The three above mentioned functions are all you need for safe memory management.
 
 A `Var<Value>` has a property `value: Value`. If `Value` conforms to `Equatable` or `Comparable`, the whole `Var<Value>` will also conform to the respective protocol.
 
-## Set Variable Values
+## Use Variable Values
 
 You can set `value` directly, via initializer and via the `<-` operator:
 
@@ -199,15 +199,15 @@ If `Value` is either `Int`, `Float` or `Double`:
 3. ```swift
     let numVar = Var<Int?>()     // numVar.value == nil
     print(numVar.int)            // 0
-    numVar <- Var(3) + 2         // numVar.value == 5
-    numVar.int += 5              // numVar.value == 10
+    numVar.int += 5              // numVar.value == 5
+    numVar <- Var(1) + 2         // numVar.value == 3
     ```
 
 ### String Values
 
 1. Every `Var<String>`, `Var<String?>`, `Var<String>?` and `Var<String?>?` has a `var string: String` which is non-optional and interprets `nil` values as `""`.
 2. Representing its `string` property, every `Var<String>` and `Var<String?>` conforms to `BidirectionalCollection`, `Collection` and `Sequence`.
-3. You can apply concatenation operators `+` and `+=` to all pairs of `String`, `String?`, `Var<String>`, `Var<String?>`, `Var<String>?` and `Var<String?>?`.
+3. You can apply concatenation operator `+` to all pairs of `String`, `String?`, `Var<String>`, `Var<String?>`, `Var<String>?` and `Var<String?>?`.
 
 ## Observe Variables
 

Tests/SwiftObserverTests/SwiftObserverTests.swift

@@ -4,6 +4,16 @@ import Foundation
 
 class SwiftObserverTests: XCTestCase
 {
+    func testStringProperty()
+    {
+        let text = Var("")
+        
+        text.string += "append"
+        
+        XCTAssertEqual("append", text.value)
+        
+    }
+    
     func testWeakMappingSource()
     {
         let toString = Weak(Var<Int?>()).new().unwrap(0).map { "\($0)" }