Merge pull request #7 from timsearle/ignoring-duplicates

Adding ignoringDuplicates Output transformer and the associated tests

Author: mikezs

Bind.xcodeproj/project.pbxproj

@@ -922,6 +922,7 @@
 			isa = XCBuildConfiguration;
 			buildSettings = {
 				BUNDLE_LOADER = "$(TEST_HOST)";
+				INFOPLIST_FILE = "";
 				LD_RUNPATH_SEARCH_PATHS = (
 					"$(inherited)",
 					"@executable_path/Frameworks",
@@ -1078,6 +1079,7 @@
 			buildSettings = {
 				BUNDLE_LOADER = "$(TEST_HOST)";
 				ENABLE_BITCODE = YES;
+				INFOPLIST_FILE = "$(SRCROOT)/Sources/Info.plist";
 				LD_RUNPATH_SEARCH_PATHS = (
 					"$(inherited)",
 					"@executable_path/Frameworks",
@@ -1212,6 +1214,7 @@
 			isa = XCBuildConfiguration;
 			buildSettings = {
 				BUNDLE_LOADER = "$(TEST_HOST)";
+				INFOPLIST_FILE = "";
 				LD_RUNPATH_SEARCH_PATHS = (
 					"$(inherited)",
 					"@executable_path/Frameworks",
@@ -1288,6 +1291,7 @@
 			buildSettings = {
 				BUNDLE_LOADER = "$(TEST_HOST)";
 				ENABLE_BITCODE = YES;
+				INFOPLIST_FILE = "$(SRCROOT)/Sources/Info.plist";
 				LD_RUNPATH_SEARCH_PATHS = (
 					"$(inherited)",
 					"@executable_path/Frameworks",

Sources/Bind/Output.swift

@@ -71,9 +71,11 @@ public class Output<Value>: Unbindable {
     /**
      `initial` allows the caller to specify an initial value to be populated into the Output through another mechanism
      other than the initialiser. If a value is already populated, this function just returns the receiver without doing
-     anything
+     anything.
      - Parameter value: The initial value
      - Returns: The same Output but with the initial value populated
+     - Note: This is useful when needing to setup a functional chain with an initial value that does not
+             trigger the chain to occur, e.g. setting the initial value at the end.
      */
     public func initial(_ value: Value) -> Output<Value> {
         if self.value == nil {
@@ -241,3 +243,27 @@ public extension Output {
         return output
     }
 }
+
+public extension Output where Value: Equatable {
+
+    /**
+     Returns a new output that filters out any contiguous repeating `Value`.
+     - Returns: A new `Output` which only emits a new value, when the new value is not equal to the previous value
+     */
+    func ignoringDuplicates() -> Output<Value> {
+        let output = Output<Value>()
+
+        var initial = self.value
+
+        let filtered = filter { value in
+            value != initial
+        }
+
+        filtered.bind { new in
+            initial = self.value
+            output.update(withValue: new)
+        }
+
+        return filtered
+    }
+}

Tests/BindTests/OutputTests.swift

@@ -333,6 +333,39 @@ final class OutputTests: XCTestCase {
         XCTAssertEqual(combined.latest, 10)
     }
 
+    func testIgnoringDuplicates() {
+        let output = Output<Bool>()
+
+        var callCounter = 0
+        var lastValue: Bool?
+
+        output
+            .ignoringDuplicates()
+            .bind { value in
+                XCTAssertNotEqual(lastValue, value)
+                lastValue = value
+                callCounter += 1
+            }
+
+        output.update(withValue: true)
+        output.update(withValue: true)
+        output.update(withValue: true)
+        XCTAssertEqual(callCounter, 1)
+
+        output.update(withValue: false)
+        XCTAssertEqual(callCounter, 2)
+
+        output.update(withValue: true)
+        output.update(withValue: true)
+        output.update(withValue: true)
+        XCTAssertEqual(callCounter, 3)
+
+        output.update(withValue: false)
+        output.update(withValue: false)
+        output.update(withValue: false)
+        XCTAssertEqual(callCounter, 4)
+    }
+
     func testDebug() {
         let printer = PrinterMock()
         let output1 = Output<Bool>(printer: printer)