How to build an Object array out of JSON array using Javascript overlay types?

My JSON response is an array of Object (Folder for example). I would like to generate an array of Folder objects using Javascript overlay types.

I tried the following method:

public static final native Folder[] buildFoldersArray(String json) /*-{
    return eval('(' + json + ')');
}-*/;

And the usage:

Folder[] folders = Folder.buildFoldersArray(myJSON);

Note: Folder extends JavaScriptObject as it should.

And the error I get:

java.lang.ClassCastException: com.google.gwt.core.client.JavaScriptObject$ cannot be cast to [Lcom.cnario.project.client.Folder;
    at com.cnario.project.client.Folder$.buildFoldersArray(Folder.java)
    at com.cnario.project.client.view.TreeView.FillTree(TreeView.java:51)
    at com.cnario.project.client.ManageContent$1.onResponseReceived(ManageContent.java:89)
    at com.google.gwt.http.client.Request.fireOnResponseReceived(Request.java:287)
    at com.google.gwt.http.client.RequestBuilder$1.onReadyStateChange(RequestBuilder.java:395)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Sou开发者_JAVA百科rce)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at com.google.gwt.dev.shell.MethodAdaptor.invoke(MethodAdaptor.java:103)
    at com.google.gwt.dev.shell.MethodDispatch.invoke(MethodDispatch.java:71)
    at com.google.gwt.dev.shell.OophmSessionHandler.invoke(OophmSessionHandler.java:172)
    at com.google.gwt.dev.shell.BrowserChannelServer.reactToMessagesWhileWaitingForReturn(BrowserChannelServer.java:337)
    at com.google.gwt.dev.shell.BrowserChannelServer.invokeJavascript(BrowserChannelServer.java:218)
    at com.google.gwt.dev.shell.ModuleSpaceOOPHM.doInvoke(ModuleSpaceOOPHM.java:136)
    at com.google.gwt.dev.shell.ModuleSpace.invokeNative(ModuleSpace.java:561)
    at com.google.gwt.dev.shell.ModuleSpace.invokeNativeObject(ModuleSpace.java:269)
    at com.google.gwt.dev.shell.JavaScriptHost.invokeNativeObject(JavaScriptHost.java:91)
    at com.google.gwt.core.client.impl.Impl.apply(Impl.java)
    at com.google.gwt.core.client.impl.Impl.entry0(Impl.java:213)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at com.google.gwt.dev.shell.MethodAdaptor.invoke(MethodAdaptor.java:103)
    at com.google.gwt.dev.shell.MethodDispatch.invoke(MethodDispatch.java:71)
    at com.google.gwt.dev.shell.OophmSessionHandler.invoke(OophmSessionHandler.java:172)
    at com.google.gwt.dev.shell.BrowserChannelServer.reactToMessages(BrowserChannelServer.java:292)
    at com.google.gwt.dev.shell.BrowserChannelServer.processConnection(BrowserChannelServer.java:546)
    at com.google.gwt.dev.shell.BrowserChannelServer.run(BrowserChannelServer.java:363)
    at java.lang.Thread.run(Unknown Source)

What is the right way of retrieving objects array using JS Overlay types?

Problem solved: evaluation should return JsArrey<E> instead of E[]:

public static final native JsArray<Folder> buildFoldersArray(String json) /*-{      
    return eval('(' + json + ')');
}-*/;

Example usage:

JsArray<Folder> folder = Folder.buildFoldersArray(json);
item = new TreeItem(folder.get(0).getName());