Hey guys, I am a little bit confused about class methods vs instance methods. for example we have a calculator. Pushing the operands and the operations from the screen into stack for further calculation, can be done by both way. I mean, each way could work perfectly. Even for some private data, we could use MutableArray Copy. My question is how do we choose if it is class mthd or instance mthd, when we want to create our own method? I mean, not those methods who create an obj, or change this variable into an obj type. Just simply our function, like "take this operation/operand sequence and do the calculation". In what circumstance shall we create a class method.