Error: 'indexing' is not a member of 'torch'

I use libtorch in https://download.pytorch.org/libtorch/cu92/libtorch-cxx11-abi-shared-with-deps-1.4.0%2Bcu92.zip

when thy to use torch::index, the compiler complains that:
error: ‘indexing’ is not a member of ‘torch’

why is that?