How to find the active scheme of a project/workspace

[Saafo]

Similar to the problem I've described on stackoverflow

There're only somethings like:

Xcodeproj::Workspace.new_from_xcworkspace("My.xcworkspace").schemes
Xcodeproj::Project.schemes("My.xcodeproj")

What I want is: Xcodeproj::Project.active_scheme("My.xcodeproj")