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Erasure: how we got the generics we have, or how I learned to stop worrying and love erasure (cr.openjdk.org)

submitted 1 year ago by [email protected] to c/[email protected]

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A great read for folks wondering why Java uses type erasure instead of "reified" generics. For the unaware, that means that a List<Integer> is a List<Object> at runtime. I had always wondered about it and why they didn't take the alternative route. For context, C# does have reified types so the actual type parameter is available at runtime.

I personally love reading in depth discussions about counter intuitive engineering decisions like this.

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[–] [email protected] 1 points 1 year ago (1 children)

This is an interesting read, but it doesn’t really live up to the title. I can see how erasure was the best compromise at the time, but it’s still a compromise.

[–] [email protected] 2 points 1 year ago

Yeah, this quote pretty much sums it up

C# made the opposite choice – to update their VM, and invalidate their existing libraries and all the user code that dependend on it. They could do this at the time because there was comparatively little C# code in the world; Java didn’t have this option at the time.

Which tells me that it was mostly about maintaing backwards compatibility with legacy code. Having used C# and Java for years the effect of type erasure seems to be bunch of silly @SuppressWarnings("unchecked") annotations in code and classes that mostly just exist to encapsulate a list of objects. With C# I create my own generics all the time but with Java I tend to avoid doing that like a plague.

I do however have to admit that I skimmed through most of the article because it's just too difficult to read with its complex vocabulary (full of words like pragmatic, ubiquitous, fictions, heterogeneous, etc) combined with a lot of technical jargon about lower level languages. Guess reading and actually really understanding the article would be easier and less time consuming if I was native english speaker but at its current form the article is far from being accessible or succesful explaining why one should love type-erasure.

[–] [email protected] 0 points 1 year ago

I've always wondered, if it's also just less pain when you write plain/idiomatic Java.

I write mostly functional Scala with lots of message passing and such, so data types often move through interfaces where their type may be lost and then we do lots of pattern matching, where missing runtime types come up on quite a regular basis.

I'd say probably once a week, I have to write or come by an ugly portion of code where we had to manually pass around type information and do explicit casts to make it all fit together.