core: use reference equality for null checks where possible

core/js/src/main/scala/zio/internal/metrics/ConcurrentMetricHooksPlatformSpecific.scala

@@ -120,7 +120,7 @@ private[zio] class ConcurrentMetricHooksPlatformSpecific extends ConcurrentMetri
 
       for (idx <- 0 until maxSize) {
         val item = values(idx)
-        if (item != null) {
+        if (item ne null) {
           val (t, v) = item
           val age    = Duration.fromInterval(t, now)
           if (!age.isNegative && age.compareTo(maxAge) <= 0) {

core/jvm/src/main/scala/zio/internal/OneElementConcurrentQueue.scala

@@ -54,7 +54,7 @@ private[zio] final class OneElementConcurrentQueue[A] extends MutableConcurrentQ
   override def enqueuedCount(): Long =
     if (isEmpty()) dequeuedCount() else dequeuedCount() + 1
 
-  override def isEmpty(): Boolean = ref.get() == null
+  override def isEmpty(): Boolean = ref.get() eq null
   override def isFull(): Boolean  = !isEmpty()
 
   override def offer(a: A): Boolean = {
@@ -65,7 +65,7 @@ private[zio] final class OneElementConcurrentQueue[A] extends MutableConcurrentQ
     var looping = true
 
     while (looping) {
-      if (aRef.get() != null) looping = false
+      if (aRef.get() ne null) looping = false
       else {
         if (aRef.compareAndSet(null, a.asInstanceOf[AnyRef])) {
           ret = true
@@ -85,7 +85,7 @@ private[zio] final class OneElementConcurrentQueue[A] extends MutableConcurrentQ
 
     while (looping) {
       el = aRef.get()
-      if (el == null) looping = false
+      if (el eq null) looping = false
       else {
         if (aRef.compareAndSet(el, null)) {
           ret = el.asInstanceOf[A]

core/jvm/src/main/scala/zio/internal/OneShot.scala

@@ -41,7 +41,7 @@ private[zio] final class OneShot[A] private () extends ReentrantLock(false) {
     this.lock()
 
     try {
-      if (value != null) throw new Error("Defect: OneShot variable being set twice")
+      if (value ne null) throw new Error("Defect: OneShot variable being set twice")
 
       value = v.asInstanceOf[A with AnyRef]
 
@@ -54,7 +54,7 @@ private[zio] final class OneShot[A] private () extends ReentrantLock(false) {
   /**
    * Determines if the variable has been set.
    */
-  def isSet: Boolean = value != null
+  def isSet: Boolean = value ne null
 
   /**
    * Retrieves the value of the variable, blocking if necessary.
@@ -70,12 +70,12 @@ private[zio] final class OneShot[A] private () extends ReentrantLock(false) {
       this.lock()
 
       try {
-        if (value == null) this.isSetCondition.await(timeout, java.util.concurrent.TimeUnit.MILLISECONDS)
+        if (value eq null) this.isSetCondition.await(timeout, java.util.concurrent.TimeUnit.MILLISECONDS)
       } finally {
         this.unlock()
       }
 
-      if (value == null) throw new Error("Timed out waiting for variable to be set")
+      if (value eq null) throw new Error("Timed out waiting for variable to be set")
 
       value
     }
@@ -91,7 +91,7 @@ private[zio] final class OneShot[A] private () extends ReentrantLock(false) {
       this.lock()
 
       try {
-        while (value == null) this.isSetCondition.await()
+        while (value eq null) this.isSetCondition.await()
       } finally {
         this.unlock()
       }

core/jvm/src/main/scala/zio/internal/metrics/ConcurrentMetricHooksPlatformSpecific.scala

@@ -158,7 +158,7 @@ private[zio] class ConcurrentMetricHooksPlatformSpecific extends ConcurrentMetri
 
       for (idx <- 0 until maxSize) {
         val item = values.get(idx)
-        if (item != null) {
+        if (item ne null) {
           val (v, t) = item
           val age    = Duration.fromInterval(t, now)
           if (!age.isNegative && age.compareTo(maxAge) <= 0) {

core/jvm/src/main/scala/zio/metrics/jvm/Thread.scala

@@ -27,7 +27,7 @@ object Thread {
       allThreads <- ZIO.attempt(threadMXBean.getThreadInfo(threadMXBean.getAllThreadIds, 0))
       initial     = java.lang.Thread.State.values().map(_ -> 0L).toMap
       result = allThreads.foldLeft(initial) { (result, thread) =>
-                 if (thread != null) {
+                 if (thread ne null) {
                    result.updated(thread.getThreadState, result(thread.getThreadState) + 1)
                  } else result
                }

core/native/src/main/scala/zio/internal/OneShot.scala

@@ -29,22 +29,22 @@ private[zio] final class OneShot[A] private (var value: A) {
    * if the variable has already been set.
    */
   def set(v: A): Unit = {
-    if (v == null) throw new Error("Defect: OneShot variable cannot be set to null value")
-    if (value != null) throw new Error("Defect: OneShot variable being set twice")
+    if (v eq null) throw new Error("Defect: OneShot variable cannot be set to null value")
+    if (value ne null) throw new Error("Defect: OneShot variable being set twice")
     value = v
   }
 
   /**
    * Determines if the variable has been set.
    */
-  def isSet: Boolean = value != null
+  def isSet: Boolean = value ne null
 
   /**
    * Retrieves the value of the variable, blocking if necessary.
    */
   def get(): A = {
-    if (value == null) scala.scalanative.loop.EventLoop.run()
-    if (value == null) throw new Error("Cannot block for result to be set in Scala Native")
+    if (value eq null) scala.scalanative.loop.EventLoop.run()
+    if (value eq null) throw new Error("Cannot block for result to be set in Scala Native")
     value
   }
 

core/native/src/main/scala/zio/internal/metrics/ConcurrentMetricHooksPlatformSpecific.scala

@@ -120,7 +120,7 @@ private[zio] class ConcurrentMetricHooksPlatformSpecific extends ConcurrentMetri
 
       for (idx <- 0 until maxSize) {
         val item = values(idx)
-        if (item != null) {
+        if (item ne null) {
           val (t, v) = item
           val age    = Duration.fromInterval(t, now)
           if (!age.isNegative && age.compareTo(maxAge) <= 0) {

core/shared/src/main/scala-2.12/zio/ChunkLike.scala

@@ -174,14 +174,14 @@ private[zio] trait ChunkLike[+A]
       val bs    = f(a)
       val chunk = ChunkLike.fromGenTraversableOnce(bs)
       if (chunk.length > 0) {
-        if (B0 == null) {
+        if (B0 eq null) {
           B0 = Chunk.classTagOf(chunk)
         }
         chunks ::= chunk
         total += chunk.length
       }
     }
-    if (B0 == null) Chunk.empty
+    if (B0 eq null) Chunk.empty
     else {
       implicit val B: ClassTag[B] = B0
       val dest: Array[B]          = Array.ofDim(total)

core/shared/src/main/scala-2.13+/zio/ChunkLike.scala

@@ -78,14 +78,14 @@ trait ChunkLike[+A]
       val bs    = f(a)
       val chunk = Chunk.from(bs)
       if (chunk.length > 0) {
-        if (B0 == null) {
+        if (B0 eq null) {
           B0 = Chunk.classTagOf(chunk)
         }
         chunks ::= chunk
         total += chunk.length
       }
     }
-    if (B0 == null) Chunk.empty
+    if (B0 eq null) Chunk.empty
     else {
       implicit val B: ClassTag[B] = B0
       val dest: Array[B]          = Array.ofDim(total)

core/shared/src/main/scala/zio/Runtime.scala

@@ -161,7 +161,7 @@ trait Runtime[+R] { self =>
 
       val exit = fiber.start[R](zio)
 
-      if (exit != null) Right(exit)
+      if (exit ne null) Right(exit)
       else {
         FiberScope.global.add(null, runtimeFlags, fiber)
         Left(fiber)

core/shared/src/main/scala/zio/ZLogger.scala

@@ -138,7 +138,7 @@ object ZLogger {
       .append(message0())
       .append("\"")
 
-    if (cause != null && cause != Cause.empty) {
+    if ((cause ne null) && cause != Cause.empty) {
       sb.append(" cause=\"")
         .append(cause.prettyPrint)
         .append("\"")

core/shared/src/main/scala/zio/internal/ConcurrentWeakHashSet.scala

@@ -378,19 +378,19 @@ private[zio] class ConcurrentWeakHashSet[V](
         case UpdateOperation.None =>
           false
         case UpdateOperation.AddElement =>
-          if (matchedRef == null) {
+          if (matchedRef eq null) {
             val newRef = new RefNode[V](element, hash, true, this.queue, head)
             this.references(index) = newRef
             this.counter.incrementAndGet()
             true
           } else false
         case UpdateOperation.RemoveElement =>
-          if (matchedRef != null) {
+          if (matchedRef ne null) {
             var previousRef = null.asInstanceOf[RefNode[V]]
             var currentRef  = head
             while (currentRef ne null) {
               if (currentRef == matchedRef) {
-                if (previousRef == null) {
+                if (previousRef eq null) {
                   this.references(index) = currentRef.nextRefNode // start chain with next ref
                 } else {
                   previousRef.nextRefNode = currentRef.nextRefNode // skip current ref
@@ -532,7 +532,7 @@ private[zio] class ConcurrentWeakHashSet[V](
     private def moveToNextReferenceIfNecessary(): Unit =
       while (this.nextElement == null) {
         moveToNextReference()
-        if (this.reference == null) return
+        if (this.reference eq null) return
         this.nextElement = this.reference.get()
       }
 
@@ -544,7 +544,7 @@ private[zio] class ConcurrentWeakHashSet[V](
       if (this.reference ne null) {
         this.reference = this.reference.nextRefNode
       }
-      while (this.reference == null && (this.references ne null)) {
+      while ((this.reference eq null) && (this.references ne null)) {
         if (this.referenceIndex >= this.references.length) {
           this.moveToNextSegment()
           this.referenceIndex = 0

core/shared/src/main/scala/zio/internal/FiberRuntime.scala

@@ -1253,7 +1253,7 @@ final class FiberRuntime[E, A](fiberId: FiberId.Runtime, fiberRefs0: FiberRefs,
   private def sendInterruptSignalToAllChildren(
     children: JavaSet[Fiber.Runtime[_, _]]
   ): Boolean =
-    if (children == null || children.isEmpty) false
+    if ((children eq null) || children.isEmpty) false
     else {
       // Initiate asynchronous interruption of all children:
       val iterator = children.iterator()

core/shared/src/main/scala/zio/internal/PinchableArray.scala

@@ -90,7 +90,7 @@ private[zio] final class PinchableArray[A: ClassTag](hint: Int) extends Iterable
   }
 
   private[zio] def asChunk(): Chunk[A] =
-    if (array == null) Chunk.empty
+    if (array eq null) Chunk.empty
     else Chunk.fromArray(array).take(_size)
 
   private def ensurePinchCapacity(newSize: Int): Unit =

core/shared/src/main/scala/zio/internal/Stack.scala

@@ -50,7 +50,7 @@ private[zio] final class Stack[A <: AnyRef]() extends Iterable[A] { self =>
 
         var result = null.asInstanceOf[A]
 
-        while (result == null && currentIndex >= 0) {
+        while ((result eq null) && currentIndex >= 0) {
           result = computeNext()
         }
 

core/shared/src/main/scala/zio/internal/WeakConcurrentBag.scala

@@ -151,18 +151,18 @@ private[zio] class WeakConcurrentBag[A <: AnyRef](nurserySize: Int, isAlive: IsA
         if (it.hasNext) {
           val next = it.next().get()
 
-          if (next == null) {
+          if (next eq null) {
             it.remove() // Remove dead reference since we're iterating over the set
             prefetch()
           } else next
         } else {
           null.asInstanceOf[A]
         }
 
-      def hasNext() = _next != null
+      def hasNext() = _next ne null
 
       def next(): A =
-        if (_next == null)
+        if (_next eq null)
           throw new NoSuchElementException("There is no more element in the weak concurrent bag iterator")
         else {
           val result = _next

core/shared/src/main/scala/zio/internal/metrics/ConcurrentMetricRegistry.scala

@@ -35,7 +35,7 @@ private[zio] class ConcurrentMetricRegistry {
 
     var hook0: MetricHook[_, zio.metrics.MetricState.Untyped] = map.get(key)
 
-    if (hook0 == null) {
+    if (hook0 eq null) {
       (key.keyType match {
         case MetricKeyType.Counter             => getCounter(key.asInstanceOf[MetricKey.Counter])
         case MetricKeyType.Frequency           => getSetCount(key.asInstanceOf[MetricKey.Frequency])
@@ -47,7 +47,7 @@ private[zio] class ConcurrentMetricRegistry {
   }
 
   def remove[Type <: MetricKeyType](key: MetricKey[Type])(implicit unsafe: Unsafe): Boolean =
-    map.remove(key) != null
+    map.remove(key) ne null
 
   @tailrec
   final def addListener(listener: MetricListener)(implicit unsafe: Unsafe): Unit = {