diff --git a/compiler/frontend/src/org/jetbrains/jet/lang/resolve/calls/CallResolver.java b/compiler/frontend/src/org/jetbrains/jet/lang/resolve/calls/CallResolver.java
index 739652befb0..d1aed5c2534 100644
--- a/compiler/frontend/src/org/jetbrains/jet/lang/resolve/calls/CallResolver.java
+++ b/compiler/frontend/src/org/jetbrains/jet/lang/resolve/calls/CallResolver.java
@@ -97,13 +97,13 @@ public class CallResolver {
         assert calleeExpression instanceof JetSimpleNameExpression;
         JetSimpleNameExpression nameExpression = (JetSimpleNameExpression) calleeExpression;
         Name referencedName = nameExpression.getReferencedNameAsName();
-        List<CallableDescriptorCollector<? extends VariableDescriptor>> callableDescriptorCollectors = Lists.newArrayList();
+        CallableDescriptorCollectors<VariableDescriptor> callableDescriptorCollectors;
         if (nameExpression.getReferencedNameElementType() == JetTokens.FIELD_IDENTIFIER) {
             referencedName = Name.identifier(referencedName.asString().substring(1));
-            callableDescriptorCollectors.add(CallableDescriptorCollectors.PROPERTIES);
+            callableDescriptorCollectors = CallableDescriptorCollectors.PROPERTIES;
         }
         else {
-            callableDescriptorCollectors.add(CallableDescriptorCollectors.VARIABLES);
+            callableDescriptorCollectors = CallableDescriptorCollectors.VARIABLES;
         }
         TracingStrategy tracing = TracingStrategyImpl.create(nameExpression, context.call);
         List<ResolutionTask<VariableDescriptor, VariableDescriptor>> prioritizedTasks =
@@ -142,9 +142,7 @@ public class CallResolver {
             @NotNull BasicCallResolutionContext context,
             @NotNull TracingStrategy tracing
     ) {
-        List<CallableDescriptorCollector<? extends CallableDescriptor>> collectors = Collections
-                .<CallableDescriptorCollector<? extends CallableDescriptor>>singletonList(CallableDescriptorCollectors.FUNCTIONS);
-        return resolveCallWithGivenName(context, Name.identifier("invoke"), tracing, collectors);
+        return resolveCallWithGivenName(context, Name.identifier("invoke"), tracing, CallableDescriptorCollectors.FUNCTIONS);
     }
 
     @NotNull
@@ -152,7 +150,7 @@ public class CallResolver {
             @NotNull BasicCallResolutionContext context,
             @NotNull Name name,
             @NotNull TracingStrategy tracing,
-            @NotNull List<CallableDescriptorCollector<? extends CallableDescriptor>> collectors
+            @NotNull CallableDescriptorCollectors<CallableDescriptor> collectors
     ) {
         List<ResolutionTask<CallableDescriptor, FunctionDescriptor>> tasks =
                 TaskPrioritizer.<CallableDescriptor, FunctionDescriptor>computePrioritizedTasks(context, name, tracing, collectors);
diff --git a/compiler/frontend/src/org/jetbrains/jet/lang/resolve/calls/tasks/CallableDescriptorCollectors.java b/compiler/frontend/src/org/jetbrains/jet/lang/resolve/calls/tasks/CallableDescriptorCollectors.java
index 78230ecbf2f..5d1e88f60c3 100644
--- a/compiler/frontend/src/org/jetbrains/jet/lang/resolve/calls/tasks/CallableDescriptorCollectors.java
+++ b/compiler/frontend/src/org/jetbrains/jet/lang/resolve/calls/tasks/CallableDescriptorCollectors.java
@@ -30,15 +30,23 @@ import java.util.*;
 
 import static org.jetbrains.jet.lang.resolve.LibrarySourceHacks.filterOutMembersFromLibrarySource;
 
-public class CallableDescriptorCollectors {
-    public static CallableDescriptorCollector<FunctionDescriptor> FUNCTIONS =
+@SuppressWarnings("unchecked")
+public class CallableDescriptorCollectors<D extends CallableDescriptor> implements Iterable<CallableDescriptorCollector<D>> {
+    private static final CallableDescriptorCollector<FunctionDescriptor> FUNCTIONS_COLLECTOR =
             new FilteredCollector<FunctionDescriptor>(new FunctionCollector());
-    public static CallableDescriptorCollector<VariableDescriptor> VARIABLES =
+    private static final CallableDescriptorCollector<VariableDescriptor> VARIABLES_COLLECTOR =
             new FilteredCollector<VariableDescriptor>(new VariableCollector());
-    public static CallableDescriptorCollector<VariableDescriptor> PROPERTIES =
+    private static final CallableDescriptorCollector<VariableDescriptor> PROPERTIES_COLLECTOR =
             new FilteredCollector<VariableDescriptor>(new PropertyCollector());
-    public static List<CallableDescriptorCollector<? extends CallableDescriptor>> FUNCTIONS_AND_VARIABLES =
-            Lists.newArrayList(FUNCTIONS, VARIABLES);
+
+    public static final CallableDescriptorCollectors<CallableDescriptor> FUNCTIONS_AND_VARIABLES =
+            new CallableDescriptorCollectors(FUNCTIONS_COLLECTOR, VARIABLES_COLLECTOR);
+    public static final CallableDescriptorCollectors<CallableDescriptor> FUNCTIONS =
+            new CallableDescriptorCollectors(FUNCTIONS_COLLECTOR);
+    public static final CallableDescriptorCollectors<VariableDescriptor> VARIABLES =
+            new CallableDescriptorCollectors(VARIABLES_COLLECTOR);
+    public static final CallableDescriptorCollectors<VariableDescriptor> PROPERTIES =
+            new CallableDescriptorCollectors(PROPERTIES_COLLECTOR);
 
     private static class FunctionCollector implements CallableDescriptorCollector<FunctionDescriptor> {
 
@@ -145,19 +153,19 @@ public class CallableDescriptorCollectors {
         @NotNull
         @Override
         public Collection<VariableDescriptor> getNonExtensionsByName(JetScope scope, Name name, @NotNull BindingTrace bindingTrace) {
-            return filterProperties(VARIABLES.getNonExtensionsByName(scope, name, bindingTrace));
+            return filterProperties(VARIABLES_COLLECTOR.getNonExtensionsByName(scope, name, bindingTrace));
         }
 
         @NotNull
         @Override
         public Collection<VariableDescriptor> getMembersByName(@NotNull JetType receiver, Name name, @NotNull BindingTrace bindingTrace) {
-            return filterProperties(VARIABLES.getMembersByName(receiver, name, bindingTrace));
+            return filterProperties(VARIABLES_COLLECTOR.getMembersByName(receiver, name, bindingTrace));
         }
 
         @NotNull
         @Override
         public Collection<VariableDescriptor> getNonMembersByName(JetScope scope, Name name, @NotNull BindingTrace bindingTrace) {
-            return filterProperties(VARIABLES.getNonMembersByName(scope, name, bindingTrace));
+            return filterProperties(VARIABLES_COLLECTOR.getNonMembersByName(scope, name, bindingTrace));
         }
 
         @Override
@@ -197,6 +205,15 @@ public class CallableDescriptorCollectors {
         }
     }
 
-    private CallableDescriptorCollectors() {
+    private final Collection<CallableDescriptorCollector<D>> collectors;
+
+    private CallableDescriptorCollectors(CallableDescriptorCollector<D>... collectors) {
+        this.collectors = Lists.newArrayList(collectors);
+    }
+
+    @NotNull
+    @Override
+    public Iterator<CallableDescriptorCollector<D>> iterator() {
+        return collectors.iterator();
     }
 }
diff --git a/compiler/frontend/src/org/jetbrains/jet/lang/resolve/calls/tasks/TaskPrioritizer.java b/compiler/frontend/src/org/jetbrains/jet/lang/resolve/calls/tasks/TaskPrioritizer.java
index 91cbc230255..39eb7ff3f84 100644
--- a/compiler/frontend/src/org/jetbrains/jet/lang/resolve/calls/tasks/TaskPrioritizer.java
+++ b/compiler/frontend/src/org/jetbrains/jet/lang/resolve/calls/tasks/TaskPrioritizer.java
@@ -81,7 +81,7 @@ public class TaskPrioritizer {
             @NotNull BasicCallResolutionContext context,
             @NotNull Name name,
             @NotNull TracingStrategy tracing,
-            @NotNull List<CallableDescriptorCollector<? extends D>> callableDescriptorCollectors
+            @NotNull CallableDescriptorCollectors<D> callableDescriptorCollectors
     ) {
         List<Pair<JetScope, ReceiverValue>> variants = new ArrayList<Pair<JetScope, ReceiverValue>>(2);
 
@@ -136,10 +136,10 @@ public class TaskPrioritizer {
         List<JetType> variantsForExplicitReceiver = AutoCastUtils.getAutoCastVariants(explicitReceiver, c.context);
 
         //members
-        for (CallableDescriptorCollector<? extends D> callableDescriptorCollector : c.callableDescriptorCollectors) {
+        for (CallableDescriptorCollector<D> callableDescriptorCollector : c.callableDescriptorCollectors) {
             Collection<ResolutionCandidate<D>> members = Lists.newArrayList();
             for (JetType type : variantsForExplicitReceiver) {
-                Collection<? extends D> membersForThisVariant =
+                Collection<D> membersForThisVariant =
                         callableDescriptorCollector.getMembersByName(type, c.name, c.context.trace);
                 convertWithReceivers(membersForThisVariant, explicitReceiver,
                                      NO_RECEIVER, members, createKind(THIS_OBJECT, isExplicit), c.context.call);
@@ -147,7 +147,7 @@ public class TaskPrioritizer {
             c.result.addCandidates(members);
         }
 
-        for (CallableDescriptorCollector<? extends D> callableDescriptorCollector : c.callableDescriptorCollectors) {
+        for (CallableDescriptorCollector<D> callableDescriptorCollector : c.callableDescriptorCollectors) {
             //member extensions
             for (ReceiverValue implicitReceiver : implicitReceivers) {
                 addMemberExtensionCandidates(implicitReceiver, explicitReceiver,
@@ -169,10 +169,10 @@ public class TaskPrioritizer {
     private static <D extends CallableDescriptor, F extends D> void addMemberExtensionCandidates(
             @NotNull ReceiverValue thisObject,
             @NotNull ReceiverValue receiverParameter,
-            @NotNull CallableDescriptorCollector<? extends D> callableDescriptorCollector, TaskPrioritizerContext<D, F> c,
+            @NotNull CallableDescriptorCollector<D> callableDescriptorCollector, TaskPrioritizerContext<D, F> c,
             @NotNull ExplicitReceiverKind receiverKind
     ) {
-        Collection<? extends D> memberExtensions = callableDescriptorCollector.getNonMembersByName(
+        Collection<D> memberExtensions = callableDescriptorCollector.getNonMembersByName(
                 thisObject.getType().getMemberScope(), c.name, c.context.trace);
         c.result.addCandidates(convertWithReceivers(
                 memberExtensions, thisObject, receiverParameter, receiverKind, c.context.call));
@@ -184,7 +184,7 @@ public class TaskPrioritizer {
     ) {
         List<Collection<ResolutionCandidate<D>>> localsList = Lists.newArrayList();
         List<Collection<ResolutionCandidate<D>>> nonlocalsList = Lists.newArrayList();
-        for (CallableDescriptorCollector<? extends D> callableDescriptorCollector : c.callableDescriptorCollectors) {
+        for (CallableDescriptorCollector<D> callableDescriptorCollector : c.callableDescriptorCollectors) {
 
             Collection<ResolutionCandidate<D>> members = convertWithImpliedThisAndNoReceiver(
                     c.scope, callableDescriptorCollector.getNonExtensionsByName(c.scope, c.name, c.context.trace), c.context.call);
@@ -253,13 +253,13 @@ public class TaskPrioritizer {
             @NotNull TaskPrioritizerContext<D, F> c,
             @NotNull ExplicitReceiverKind receiverKind
     ) {
-        for (CallableDescriptorCollector<? extends D> callableDescriptorCollector : c.callableDescriptorCollectors) {
+        for (CallableDescriptorCollector<D> callableDescriptorCollector : c.callableDescriptorCollectors) {
             addMemberExtensionCandidates(thisObject, receiverParameter, callableDescriptorCollector, c, receiverKind);
         }
     }
 
     private static <D extends CallableDescriptor> Collection<ResolutionCandidate<D>> convertWithReceivers(
-            @NotNull Collection<? extends D> descriptors,
+            @NotNull Collection<D> descriptors,
             @NotNull ReceiverValue thisObject,
             @NotNull ReceiverValue receiverParameter,
             @NotNull ExplicitReceiverKind explicitReceiverKind,
@@ -271,7 +271,7 @@ public class TaskPrioritizer {
     }
 
     private static <D extends CallableDescriptor> void convertWithReceivers(
-            @NotNull Collection<? extends D> descriptors,
+            @NotNull Collection<D> descriptors,
             @NotNull ReceiverValue thisObject,
             @NotNull ReceiverValue receiverParameter,
             @NotNull Collection<ResolutionCandidate<D>> result,
@@ -383,14 +383,14 @@ public class TaskPrioritizer {
         @NotNull public final ResolutionTaskHolder<D, F> result;
         @NotNull public final BasicCallResolutionContext context;
         @NotNull public final JetScope scope;
-        @NotNull public final List<CallableDescriptorCollector<? extends D>> callableDescriptorCollectors;
+        @NotNull public final CallableDescriptorCollectors<D> callableDescriptorCollectors;
 
         private TaskPrioritizerContext(
                 @NotNull Name name,
                 @NotNull ResolutionTaskHolder<D, F> result,
                 @NotNull BasicCallResolutionContext context,
                 @NotNull JetScope scope,
-                @NotNull List<CallableDescriptorCollector<? extends D>> callableDescriptorCollectors
+                @NotNull CallableDescriptorCollectors<D> callableDescriptorCollectors
         ) {
             this.name = name;
             this.result = result;