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Comment by sunir | Hacker News Reader

I don't understand that page in the slightest, but a lot of if-cascades can be factored more cleanly using polymorphism.

http://c2.com/cgi/wiki/wiki?PolymorphismVsSelectionIdiom

(Disclaimer. I wrote the top of that wiki page in a former life.)

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However, if you already have a class type for each key

I think that's precisely what I was trying to say - polymorphism makes sense when you already have a bunch of classes to do it with, and classes which already contain lots of other fields and methods; it doesn't make sense to create a bunch of classes just to use polymorphism.

Often, though, a series of complicated if statements is hinting at a type system for your objects that hasn't yet materialized in your code. I find it's a good idea to always look at cascading if statements and switch statements and ask, "Would this be cleaner if I reified these concepts as types?"

http://en.wikipedia.org/wiki/Reification_(computer_science)

This is the single most important trick for factoring out shitty code. I cannot believe how many times reification collapsed complexity in our code base, or how not using it was the source of bugs.

If you have cascading ifs, there is a good chance there is a huge set of ifs for every place this type system is missing. Meaning, if you wanted to add another "case" to a feature, you are modifying cascading ifs in 5-10 places, not even just one.

Wrapping up all of this code into an implementation of an interface, that is "hooked in" at each contact point allows you to add a cohesive new use case by generating a new implementation of an interface, instead of "forgetting 2 places in the code" and causing massive bugs or issues because of it.

It of course, also makes it easier to test!

So to reify a type involves making an abstraction, which is odd because reify seems the inverse of making an abstraction...

The abstraction already existed in your mental model. You're reifying it by making it something the code can refer to/reflect on/pass around.

The only difficulty is naming the abstraction :)

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