1. A method comprising: by one or more computing devices, marking an object in source code of a software program written in an object-oriented scripting language, wherein marking the object is performed with a keyword; marking one or more functions in the source code of the software program; constructing a control flow graph (CFG) for the software program; and determining whether there is any path in the CFG that leads from a first node corresponding to the marked object to a second node corresponding to any marked function paired with the object.
4. The method of claim 1 , wherein the marked object is a variable.