Building the KNN Example as a static linked executable fails

[debugaftercoffee]

I am trying to build the Example KNN Classifier using CGO_ENABLE=0 so the executable is statically linked, but it fails with the error below. If I use change CGO_ENABLE=1 instead, then it builds properly. How do I build this app as a statically linked executable.

env CGO_ENABLED=0 go build -v

os/user
archive/tar
github.com/sjwhitworth/golearn/base
github.com/sjwhitworth/golearn/knn
# github.com/sjwhitworth/golearn/knn
../../go/pkg/mod/github.com/sjwhitworth/[email protected]/knn/knn.go:132:15: KNN.optimisedEuclideanPredict undefined (type *KNNClassifier has no field or method optimisedEuclideanPredict)