Comment by rj...@google.com:I'm very uncomfortable with the "Keep implementations locked down" assertion. So long as its very clear which implementations have been vetted by the GWT team, why should we prevent clients from providing their own when they judge it to be worth the performance risk?
For more information: http://code.google.com/p/google-web-toolkit/wiki/LightweightCollections -- http://groups.google.com/group/Google-Web-Toolkit-Contributors
