内容简介：⬐Nov 26, 2019 ·> Since each transform needs to perform vastly different image operations, using an enum in this case would’ve forced us to write one massive switch statement to handle each and every one of those operations — which would most
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Nov 26, 2019 · nickmqb on Lightweight API Design in Swift
> Since each transform needs to perform vastly different image operations, using an enum in this case would’ve forced us to write one massive switch statement to handle each and every one of those operations — which would most likely become somewhat of a nightmare to maintain.
I don't mean to pick on the author, but I've seen this line of reasoning a few times before. It's the same argument that has been used in the past to justify inheritance hierarchies in OOP languages. I used to believe it too. However, I don't think this is actually true. In fact, I'd argue the opposite: switch statements, if used well, are _extremely maintainable_. Even though a switch statement might handle many cases, it does not become more complex [1] by doing so. If we're concerned about the length of the individual cases, we can easily replace each one with a function call. Fundamentally, in the example from the article, we'd like to map a piece of data (the operation with its parameters) to some behavior (actually performing the operation). A switch statement is one of the simplest ways to do that.
[1] https://www.infoq.com/presentations/Simple-Made-Easy/
What you describe is called the Expression Problem [1] in programming language design and there is no simple formulaic answer on which method is better. I think you have to consider many aspects of your code's current design and possible future evolution when deciding which approach to use. For example: do you expect to have more types of transforms, or more operations/method per type of transform? It also means you can't nitpick a limited tutorial for focusing on one approach vs. the other.
Fortunately swift (as well as Rust or Kotlin) has excellent modern toolbox that includes protocol conformance and algebraic data types so you can use either one.
Keep in mind that swift protocols avoid many of the pitfalls of Java\C++ school of OOP design you might have seen before that can only express "is-a" relationships.
[1] https://en.wikipedia.org/wiki/Expression_problem
The issue is developers not learning how to use their tools.
Agreed on all points. One of the main metrics I use to assess maintainability of code is 'how many places do I need to edit to make a change?' (within the same file or worse, in other files too), 'how easy is it to find those places?' and 'how easy is it to make a change in one of those places but overlook another needed one?' On pretty much all of those counts, a single switch statement will tend to beat an inheritance hierarchy.
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