▲ | WorldMaker 2 days ago | |
It is not too bad in languages with discriminated unions. It's also not hard to fake discriminated unions in languages without them, even if you will miss some of the niceties. Rather than thinking of it as an enum, think of it as a list of contructors:
Even if the class needs all four fields, internally to represent all the possible combinations of data, there's no constructors/setters to work with them independently. (Which is also related to why "Make Impossible States Unrepresentable" also generally implies immutable, no setters at all makes it much easier to make states impossible.)In languages with discriminated unions you might even have some natural field sharing depending on how your "constructors" are written and the memory expansion isn't necessarily "exponential". | ||
▲ | crdrost a day ago | parent [-] | |
Also to mention it, languages without discriminated unions often have generics and function types, which can be used to build discriminated unions with Church encodings:
In addition the Church encoding of a sum type, is a function that takes N handler functions and calls the appropriate one for the case that the data type is in. With a little squinting, this is the Visitor pattern.
The main difference with the usual visitor pattern is that the usual visitor pattern doesn't return anything (it expects you to be holding some mutable state and the visitor will mutate it), you can do that too if you don't have access to a suitable generic for the Z parameter. |