Suppress setting the same value on object

Sources/UserInterfaceVariations/UIVariation.swift

@@ -63,17 +63,28 @@ public class UIVariation<Object: AnyObject, Value>: NSObject {
 extension UIVariation: UIVariationApplying {
     
     func applyIfMatchesTraitEnvironment() {
+        guard doesMatchTraitEnvironment() else { return }
+        object[keyPath: property] = value
+    }
+    
+    func applyIfMatchesTraitEnvironment() where Value: Equatable {
+        guard doesMatchTraitEnvironment() else { return }
+        guard object[keyPath: property] != value else { return }
+        object[keyPath: property] = value
+    }
+    
+    private func doesMatchTraitEnvironment() -> Bool {
         guard let traitCollection = traitEnvironment?.traitCollection else {
             print("Missing traitEnvironment when trying to apply \(self)")
-            return
+            return false
         }
         if let horizontalSizeClass = horizontalSizeClass {
-            if traitCollection.horizontalSizeClass != horizontalSizeClass { return }
+            if traitCollection.horizontalSizeClass != horizontalSizeClass { return false }
         }
         if let verticalSizeClass = verticalSizeClass {
-            if traitCollection.verticalSizeClass != verticalSizeClass { return }
+            if traitCollection.verticalSizeClass != verticalSizeClass { return false }
         }
-        object[keyPath: property] = value
+        return true
     }
 }
 

Tests/UserInterfaceVariationsTests/UIVariationTests.swift

@@ -85,6 +85,20 @@ final class UIVariationTests: XCTestCase {
         XCTAssertNotEqual(label.text, sut.value)
     }
     
+    func test_When_object_value_is_already_equal_to_variation_value_Then_variation_is_NOT_applied() {
+        let object = Object()
+        let sut = UIVariation(object: object,
+                              keyPath: \.text,
+                              value: valueWhenCompact,
+                              horizontalSizeClass: .compact,
+                              verticalSizeClass: nil)
+        traitEnvironment.traitCollection = UITraitCollection(horizontalSizeClass: .compact)
+        sut.traitEnvironment = traitEnvironment
+        sut.applyIfMatchesTraitEnvironment()
+        sut.applyIfMatchesTraitEnvironment()
+        XCTAssertEqual(object.setCount, 1)
+    }
+    
     func test_factory_method_for_sizeClassDimension_horizontal() {
         let variations = UIVariation.make(for: label,
                                           property: \.text,
@@ -134,3 +148,11 @@ class TraitEnvironmentStub: NSObject, UITraitEnvironment {
         
     }
 }
+
+class Object {
+    
+    var text: String? {
+        didSet { setCount += 1 }
+    }
+    var setCount = 0
+}