enable forking of Modes and add ImmutableMode

 - make sure the default empty Mode is immutable

README.md

@@ -13,7 +13,7 @@ repositories {
 }
 
 dependencies {
-    implementation "com.github.robinfriedli:exec:1.3"
+    implementation "com.github.robinfriedli:exec:1.4"
 }
 ```
 
@@ -22,7 +22,7 @@ dependencies {
 <dependency>
   <groupId>com.github.robinfriedli</groupId>
   <artifactId>exec</artifactId>
-  <version>1.3</version>
+  <version>1.4</version>
   <type>pom</type>
 </dependency>
 

build.gradle

@@ -5,7 +5,7 @@ plugins {
 }
 
 group = "net.robinfriedli"
-version = "1.3"
+version = "1.4"
 sourceCompatibility = "8"
 targetCompatibility = "8"
 

src/main/kotlin/net/robinfriedli/exec/AbstractNestedModeWrapper.kt

@@ -9,17 +9,22 @@ abstract class AbstractNestedModeWrapper : ModeWrapper {
 
     private var outer: ModeWrapper? = null
 
-    override fun combine(mode: ModeWrapper): ModeWrapper {
+    final override fun combine(mode: ModeWrapper): ModeWrapper {
         mode.setOuter(this)
         return mode
     }
 
-    override fun getOuter(): ModeWrapper? {
+    final override fun getOuter(): ModeWrapper? {
         return outer
     }
 
-    override fun setOuter(mode: ModeWrapper?) {
+    final override fun setOuter(mode: ModeWrapper?) {
         this.outer = mode
     }
 
-}
+    override fun fork(): ModeWrapper {
+        // since this combine implementation does not modify this ModeWrapper instance it is inherently immutable
+        return this
+    }
+
+}

src/main/kotlin/net/robinfriedli/exec/Mode.kt

@@ -3,13 +3,17 @@ package net.robinfriedli.exec
 /**
  * Helper class to build a mode with the given [ModeWrapper] applied
  */
-class Mode {
+open class Mode() {
+
+    private constructor(currentWrapper: ModeWrapper?) : this() {
+        this.currentWrapper = currentWrapper
+    }
 
     private var currentWrapper: ModeWrapper? = null
 
     companion object {
         @JvmStatic
-        val empty = create()
+        val empty = create().immutable()
 
         @JvmStatic
         fun create(): Mode {
@@ -23,19 +27,49 @@ class Mode {
      * inside the task of the current wrapper.
      *
      * @param wrapper the new wrapper to add, normally wrapping it inside the current wrapper
-     * @return this mode with the new wrapper applied
+     * @return this mode with the new wrapper applied, or a new Mode instance if this Mode was immutable
      */
-    fun with(wrapper: ModeWrapper): Mode {
-        if (currentWrapper != null) {
-            currentWrapper = currentWrapper!!.combine(wrapper)
+    open fun with(wrapper: ModeWrapper): Mode {
+        currentWrapper = if (currentWrapper != null) {
+            currentWrapper!!.combine(wrapper)
         } else {
-            currentWrapper = wrapper
+            wrapper
         }
         return this
     }
 
-    fun getWrapper(): ModeWrapper? {
+    open fun getWrapper(): ModeWrapper? {
         return currentWrapper
     }
 
-}
+    /**
+     * Clone this Mode so that changes made to the returned Mode are not reflected by this instance.
+     */
+    open fun fork(): Mode {
+        return Mode(currentWrapper?.fork())
+    }
+
+    /**
+     * Wraps this Mode into a [ImmutableMode], prohibiting modifications to this instance by making calls to [Mode.with]
+     * fork the Mode by calling [Mode.fork] and operating on the cloned instance. Note that instances returned by
+     * [ImmutableMode.with] are not immutable.
+     */
+    fun immutable(): ImmutableMode {
+        return ImmutableMode(this)
+    }
+
+    class ImmutableMode(private val mode: Mode) : Mode() {
+        override fun with(wrapper: ModeWrapper): Mode {
+            return mode.fork().with(wrapper)
+        }
+
+        override fun getWrapper(): ModeWrapper? {
+            return mode.getWrapper()
+        }
+
+        override fun fork(): Mode {
+            return mode.fork()
+        }
+    }
+
+}

src/main/kotlin/net/robinfriedli/exec/ModeWrapper.kt

@@ -36,6 +36,14 @@ interface ModeWrapper : Iterable<ModeWrapper> {
 
     fun setOuter(mode: ModeWrapper?)
 
+    /**
+     * Clones this ModeWrapper for use in a new [Mode]. Changes to the returned ModeWrapper are not reflected by this instance.
+     *
+     * If the [ModeWrapper.combine] implementation does not modify this instance, meaning this implementation is practically
+     * immutable, this method does not have to do anything and can return the current instance.
+     */
+    fun fork(): ModeWrapper
+
     override fun iterator(): Iterator<ModeWrapper> {
         return object : Iterator<ModeWrapper> {
 
@@ -59,4 +67,4 @@ interface ModeWrapper : Iterable<ModeWrapper> {
 
         }
     }
-}
+}

src/test/kotlin/net/robinfriedli/exec/modes/ModesTest.kt

@@ -1,15 +1,52 @@
 package net.robinfriedli.exec.modes
 
+import net.robinfriedli.exec.AbstractNestedModeWrapper
 import net.robinfriedli.exec.Invoker
 import net.robinfriedli.exec.Mode
 import net.robinfriedli.exec.MutexSync
 import org.testng.Assert.*
+import org.testng.annotations.DataProvider
 import org.testng.annotations.Test
+import java.util.concurrent.Callable
 import java.util.concurrent.atomic.AtomicBoolean
 import java.util.concurrent.atomic.AtomicInteger
 
 class ModesTest {
 
+    @DataProvider
+    fun boolDataProvider(): Array<Any> {
+        return arrayOf(true, false)
+    }
+
+    @Test(dataProvider = "boolDataProvider")
+    fun testForkMode(immutableMode: Boolean) {
+        val mode1 = Mode
+            .create()
+            .with(AdditionModeWrapper(2))
+            .with(AdditionModeWrapper(7))
+        val mode2 = if (immutableMode) {
+            mode1.immutable()
+        } else {
+            mode1.fork()
+        }.with(AdditionModeWrapper(4))
+
+        val invoker = Invoker.defaultInstance
+        val res1 = invoker.invoke<Int>(mode1) { 3 }
+        val res2 = invoker.invoke<Int>(mode2) { 3 }
+
+        assertEquals(res1, 12)
+        assertEquals(res2, 16)
+    }
+
+    class AdditionModeWrapper(private val summand: Int) : AbstractNestedModeWrapper() {
+        override fun <T> wrap(callable: Callable<T>): Callable<T> {
+            return Callable {
+                (callable.call() as Int + summand) as T
+            }
+        }
+
+    }
+
     @Test
     fun testExceptionWrappingMode() {
         val invoker = Invoker.newInstance()