diff --git a/core/reflection.jvm/src/kotlin/reflect/KClasses.kt b/core/reflection.jvm/src/kotlin/reflect/KClasses.kt
index 2d8b15f1db4..da61d385112 100644
--- a/core/reflection.jvm/src/kotlin/reflect/KClasses.kt
+++ b/core/reflection.jvm/src/kotlin/reflect/KClasses.kt
@@ -15,6 +15,8 @@
  */
 
 @file:JvmName("KClasses")
+@file:Suppress("UNCHECKED_CAST")
+
 package kotlin.reflect
 
 import org.jetbrains.kotlin.descriptors.ConstructorDescriptor
@@ -70,7 +72,7 @@ val KClass<*>.defaultType: KType
  * Does not include members declared in supertypes.
  */
 val KClass<*>.declaredMembers: Collection<KCallable<*>>
-    get() = (this as KClassImpl).data().declaredMembers.toList()
+    get() = (this as KClassImpl).data().declaredMembers
 
 /**
  * Returns all functions declared in this class, including all non-static methods declared in the class
@@ -83,27 +85,19 @@ val KClass<*>.functions: Collection<KFunction<*>>
  * Returns static functions declared in this class.
  */
 val KClass<*>.staticFunctions: Collection<KFunction<*>>
-    get() = (this as KClassImpl).data().allStaticMembers
-            .filterIsInstance<KFunction<*>>()
-            .toList()
+    get() = (this as KClassImpl).data().allStaticMembers.filterIsInstance<KFunction<*>>()
 
 /**
  * Returns non-extension non-static functions declared in this class and all of its superclasses.
  */
 val KClass<*>.memberFunctions: Collection<KFunction<*>>
-    get() = (this as KClassImpl).data().allNonStaticMembers
-            .filterNotExtensions()
-            .filterIsInstance<KFunction<*>>()
-            .toList()
+    get() = (this as KClassImpl).data().allNonStaticMembers.filter { it.isNotExtension && it is KFunction<*> } as Collection<KFunction<*>>
 
 /**
  * Returns extension functions declared in this class and all of its superclasses.
  */
 val KClass<*>.memberExtensionFunctions: Collection<KFunction<*>>
-    get() = (this as KClassImpl).data().allNonStaticMembers
-            .filterExtensions()
-            .filterIsInstance<KFunction<*>>()
-            .toList()
+    get() = (this as KClassImpl).data().allNonStaticMembers.filter { it.isExtension && it is KFunction<*> } as Collection<KFunction<*>>
 
 /**
  * Returns all functions declared in this class.
@@ -111,80 +105,57 @@ val KClass<*>.memberExtensionFunctions: Collection<KFunction<*>>
  * declared in the class and the superclasses, as well as static methods declared in the class.
  */
 val KClass<*>.declaredFunctions: Collection<KFunction<*>>
-    get() = (this as KClassImpl).data().declaredMembers
-            .filterIsInstance<KFunction<*>>()
-            .toList()
+    get() = (this as KClassImpl).data().declaredMembers.filterIsInstance<KFunction<*>>()
 
 /**
  * Returns non-extension non-static functions declared in this class.
  */
 val KClass<*>.declaredMemberFunctions: Collection<KFunction<*>>
-    get() = (this as KClassImpl).data().declaredNonStaticMembers
-            .filterNotExtensions()
-            .filterIsInstance<KFunction<*>>()
-            .toList()
+    get() = (this as KClassImpl).data().declaredNonStaticMembers.filter { it.isNotExtension && it is KFunction<*> } as Collection<KFunction<*>>
 
 /**
  * Returns extension functions declared in this class.
  */
 val KClass<*>.declaredMemberExtensionFunctions: Collection<KFunction<*>>
-    get() = (this as KClassImpl).data().declaredNonStaticMembers
-            .filterExtensions()
-            .filterIsInstance<KFunction<*>>()
-            .toList()
+    get() = (this as KClassImpl).data().declaredNonStaticMembers.filter { it.isExtension && it is KFunction<*> } as Collection<KFunction<*>>
 
 /**
  * Returns static properties declared in this class.
  * Only properties representing static fields of Java classes are considered static.
  */
 val KClass<*>.staticProperties: Collection<KProperty0<*>>
-    get() = (this as KClassImpl).data().allStaticMembers
-            .filterNotExtensions()
-            .filterIsInstance<KProperty0<*>>()
-            .toList()
+    get() = (this as KClassImpl).data().allStaticMembers.filter { it.isNotExtension && it is KProperty0<*> } as Collection<KProperty0<*>>
 
 /**
  * Returns non-extension properties declared in this class and all of its superclasses.
  */
 val <T : Any> KClass<T>.memberProperties: Collection<KProperty1<T, *>>
-    get() = (this as KClassImpl<T>).data().allNonStaticMembers
-            .filterNotExtensions()
-            .filterIsInstance<KProperty1<T, *>>()
-            .toList()
+    get() = (this as KClassImpl<T>).data().allNonStaticMembers.filter { it.isNotExtension && it is KProperty1<*, *> } as Collection<KProperty1<T, *>>
 
 /**
  * Returns extension properties declared in this class and all of its superclasses.
  */
 val <T : Any> KClass<T>.memberExtensionProperties: Collection<KProperty2<T, *, *>>
-    get() = (this as KClassImpl<T>).data().allNonStaticMembers
-            .filterExtensions()
-            .filterIsInstance<KProperty2<T, *, *>>()
-            .toList()
+    get() = (this as KClassImpl<T>).data().allNonStaticMembers.filter { it.isExtension && it is KProperty2<*, *, *> } as Collection<KProperty2<T, *, *>>
 
 /**
  * Returns non-extension properties declared in this class.
  */
 val <T : Any> KClass<T>.declaredMemberProperties: Collection<KProperty1<T, *>>
-    get() = (this as KClassImpl<T>).data().declaredNonStaticMembers
-            .filterNotExtensions()
-            .filterIsInstance<KProperty1<T, *>>()
-            .toList()
+    get() = (this as KClassImpl<T>).data().declaredNonStaticMembers.filter { it.isNotExtension && it is KProperty1<*, *> } as Collection<KProperty1<T, *>>
 
 /**
  * Returns extension properties declared in this class.
  */
 val <T : Any> KClass<T>.declaredMemberExtensionProperties: Collection<KProperty2<T, *, *>>
-    get() = (this as KClassImpl<T>).data().declaredNonStaticMembers
-            .filterExtensions()
-            .filterIsInstance<KProperty2<T, *, *>>()
-            .toList()
+    get() = (this as KClassImpl<T>).data().declaredNonStaticMembers.filter { it.isExtension && it is KProperty2<*, *, *> } as Collection<KProperty2<T, *, *>>
 
 
-private fun <T : KCallableImpl<*>> Sequence<T>.filterExtensions(): Sequence<T> =
-        filter { it.descriptor.extensionReceiverParameter != null }
+private val KCallableImpl<*>.isExtension: Boolean
+    get() = descriptor.extensionReceiverParameter != null
 
-private fun <T : KCallableImpl<*>> Sequence<T>.filterNotExtensions(): Sequence<T> =
-        filter { it.descriptor.extensionReceiverParameter == null }
+private val KCallableImpl<*>.isNotExtension: Boolean
+    get() = !isExtension
 
 /**
  * Immediate superclasses of this class, in the order they are listed in the source code.
@@ -256,7 +227,6 @@ fun KClass<*>.isSuperclassOf(derived: KClass<*>): Boolean =
  * @see [KClass.isInstance]
  * @see [KClass.safeCast]
  */
-@Suppress("UNCHECKED_CAST")
 fun <T : Any> KClass<T>.cast(value: Any?): T {
     if (!isInstance(value)) throw TypeCastException("Value cannot be cast to $qualifiedName")
     return value as T
@@ -269,7 +239,6 @@ fun <T : Any> KClass<T>.cast(value: Any?): T {
  * @see [KClass.isInstance]
  * @see [KClass.cast]
  */
-@Suppress("UNCHECKED_CAST")
 fun <T : Any> KClass<T>.safeCast(value: Any?): T? {
     return if (isInstance(value)) value as T else null
 }
diff --git a/core/reflection.jvm/src/kotlin/reflect/jvm/internal/KClassImpl.kt b/core/reflection.jvm/src/kotlin/reflect/jvm/internal/KClassImpl.kt
index f44ba6122a7..91b4e6d1810 100644
--- a/core/reflection.jvm/src/kotlin/reflect/jvm/internal/KClassImpl.kt
+++ b/core/reflection.jvm/src/kotlin/reflect/jvm/internal/KClassImpl.kt
@@ -134,22 +134,23 @@ internal class KClassImpl<T : Any>(override val jClass: Class<T>) : KDeclaration
             }
         }
 
-        val declaredNonStaticMembers: Sequence<KCallableImpl<*>>
+        val declaredNonStaticMembers: Collection<KCallableImpl<*>>
                 by ReflectProperties.lazySoft { getMembers(memberScope, DECLARED) }
-        val declaredStaticMembers: Sequence<KCallableImpl<*>>
+        val declaredStaticMembers: Collection<KCallableImpl<*>>
                 by ReflectProperties.lazySoft { getMembers(staticScope, DECLARED) }
-        val inheritedNonStaticMembers: Sequence<KCallableImpl<*>>
+        val inheritedNonStaticMembers: Collection<KCallableImpl<*>>
                 by ReflectProperties.lazySoft { getMembers(memberScope, INHERITED) }
-        val inheritedStaticMembers: Sequence<KCallableImpl<*>>
+        val inheritedStaticMembers: Collection<KCallableImpl<*>>
                 by ReflectProperties.lazySoft { getMembers(staticScope, INHERITED) }
 
-        val allNonStaticMembers: Sequence<KCallableImpl<*>> get() = declaredNonStaticMembers + inheritedNonStaticMembers
-        val allStaticMembers: Sequence<KCallableImpl<*>> get() = declaredStaticMembers + inheritedStaticMembers
-        val declaredMembers: Sequence<KCallableImpl<*>> get() = declaredNonStaticMembers + declaredStaticMembers
-
-        val allMembers: Collection<KCallable<*>> by ReflectProperties.lazySoft {
-            (allNonStaticMembers + allStaticMembers).toList()
-        }
+        val allNonStaticMembers: Collection<KCallableImpl<*>>
+                by ReflectProperties.lazySoft { declaredNonStaticMembers + inheritedNonStaticMembers }
+        val allStaticMembers: Collection<KCallableImpl<*>>
+                by ReflectProperties.lazySoft { declaredStaticMembers + inheritedStaticMembers }
+        val declaredMembers: Collection<KCallableImpl<*>>
+                by ReflectProperties.lazySoft { declaredNonStaticMembers + declaredStaticMembers }
+        val allMembers: Collection<KCallableImpl<*>>
+                by ReflectProperties.lazySoft { allNonStaticMembers + allStaticMembers }
     }
 
     val data = ReflectProperties.lazy { Data() }
diff --git a/core/reflection.jvm/src/kotlin/reflect/jvm/internal/KDeclarationContainerImpl.kt b/core/reflection.jvm/src/kotlin/reflect/jvm/internal/KDeclarationContainerImpl.kt
index 896a714632b..7b3b9be36c0 100644
--- a/core/reflection.jvm/src/kotlin/reflect/jvm/internal/KDeclarationContainerImpl.kt
+++ b/core/reflection.jvm/src/kotlin/reflect/jvm/internal/KDeclarationContainerImpl.kt
@@ -24,6 +24,7 @@ import org.jetbrains.kotlin.load.java.structure.reflect.safeClassLoader
 import org.jetbrains.kotlin.load.kotlin.reflect.RuntimeModuleData
 import org.jetbrains.kotlin.name.Name
 import org.jetbrains.kotlin.resolve.scopes.MemberScope
+import org.jetbrains.kotlin.utils.toReadOnlyList
 import java.lang.reflect.Constructor
 import java.lang.reflect.Method
 import java.util.*
@@ -47,7 +48,7 @@ internal abstract class KDeclarationContainerImpl : ClassBasedDeclarationContain
 
     abstract fun getFunctions(name: Name): Collection<FunctionDescriptor>
 
-    protected fun getMembers(scope: MemberScope, belonginess: MemberBelonginess): Sequence<KCallableImpl<*>> {
+    protected fun getMembers(scope: MemberScope, belonginess: MemberBelonginess): Collection<KCallableImpl<*>> {
         val visitor = object : DeclarationDescriptorVisitorEmptyBodies<KCallableImpl<*>, Unit>() {
             override fun visitPropertyDescriptor(descriptor: PropertyDescriptor, data: Unit): KCallableImpl<*> =
                     createProperty(descriptor)
@@ -59,15 +60,13 @@ internal abstract class KDeclarationContainerImpl : ClassBasedDeclarationContain
                     throw IllegalStateException("No constructors should appear in this scope: $descriptor")
         }
 
-        return scope.getContributedDescriptors().asSequence()
-                .filter { descriptor ->
-                    descriptor is CallableMemberDescriptor &&
-                    descriptor.visibility != Visibilities.INVISIBLE_FAKE &&
-                    belonginess.accept(descriptor)
-                }
-                .mapNotNull { descriptor ->
-                    descriptor.accept(visitor, Unit)
-                }
+        return scope.getContributedDescriptors().mapNotNull { descriptor ->
+            if (descriptor is CallableMemberDescriptor &&
+                descriptor.visibility != Visibilities.INVISIBLE_FAKE &&
+                belonginess.accept(descriptor))
+                descriptor.accept(visitor, Unit)
+            else null
+        }.toReadOnlyList()
     }
 
     protected enum class MemberBelonginess {
diff --git a/core/reflection.jvm/src/kotlin/reflect/jvm/internal/KPackageImpl.kt b/core/reflection.jvm/src/kotlin/reflect/jvm/internal/KPackageImpl.kt
index c8d597c5c34..7c514b8fcdd 100644
--- a/core/reflection.jvm/src/kotlin/reflect/jvm/internal/KPackageImpl.kt
+++ b/core/reflection.jvm/src/kotlin/reflect/jvm/internal/KPackageImpl.kt
@@ -56,7 +56,7 @@ internal class KPackageImpl(override val jClass: Class<*>, val moduleName: Strin
                 val packageFragment = callableDescriptor.containingDeclaration as PackageFragmentDescriptor
                 val source = (packageFragment as? LazyJavaPackageFragment)?.source as? KotlinJvmBinaryPackageSourceElement
                 (source?.getContainingBinaryClass(callableDescriptor) as? ReflectKotlinClass)?.klass == jClass
-            }.toList()
+            }
         }
     }