Reduce implicit parameter passing

This rule suggests method should always use explicit parameters. In some situation, global variables are used as implicit parameter among methods within the same class. Implicit parameter ties methods with the class, and it also hide the necessary information for outsiders who wish to use the method. The results of using implicit parameter are (1) making difficult to split a class into parts, or (2) even possible to lead other programmers to miuse method (since parameters are implicit passed in which case may not be awared by other programmers).