Conversely it's really annoying to add a new method to each shape--you've got to open them all up and add shape-specific code for them with a bunch of boilerpla

Conversely it's really annoying to add a new method to each shape--you've got to open them all up and add shape-specific code for them with a bunch of boilerplate. With switch statements you just add one more function. This is the "expression problem": https://en.m.wikipedia.org/wiki/Expression_problem https://en.m.wikipedia.org/wiki/Expression_problem