OpenCV 3.0.0 beta - Use common interface with SURF

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I am trying to use the common interface to features detectors and extractors for SURF features. The documentation states that cv::SURF implements the Features2D interface, but when I try:

cv::Ptr<cv::SURF> surf = cv::SURF::create(400);

I get the compiler error:

features_analysis.cpp:134:50: error: no matching function for call to ‘cv::SURF::create(int)’

I have installed xfeatures2D from the contrib module but I am also confused about namespaces, is SURF in cv::SURF or cv::xfeatures2d::SURF ? And what is the correct header to include? The documentation is very confusing and contradictory at times.

EDIT: Is there a "beta" release of opencv_contrib? Because now I'm using opencv-3.0.0-beta with the master branch of opencv_contrib, could that be a problem?

EDIT2: Nevermind, I just found it here: https://github.com/Itseez/opencv_cont...