The jump happens when you have parameter lists too long to fit on the screen. In C++ terms, consider a const member function that returns something - you know t

The jump happens when you have parameter lists too long to fit on the screen. In C++ terms, consider a const member function that returns something - you know that it can use all the members (without having to explicitly specify each one as parameter) but not change them, so the only "mutation" it can perform is constrained to the return value (ignoring aspects like const not being transitive for pointer members). In practice I still think this doesn't work on complex algorithms because it remains unclear what depends on what.