3 ms·

I mean, I agree. The static warnings will generally steer you away from the bad cases. From a source-language standpoint, if you don't consider the second-order

by titzer 4y ago

I mean, I agree. The static warnings will generally steer you away from the bad cases. From a source-language standpoint, if you don't consider the second-order effects of this design choice, it accomplished a fair fraction of the original goals. But more complex patterns I've seen people try to pass around java.lang.Class objects as a reification. That doesn't really work, because it's skin deep. With significant experience with reified generics, there's just a lot of patterns that you can't do in Java. I wrote a whole PLDI paper about it back in 2013. Reified generics mean you can do stuff like ad-hoc polymorphism without direct language support. Ironically enough, the little trick of hiding type arguments with subtyping but getting them back with casts is a powerful dynamic tool.

kaba0 4y ago
I would be interested in your paper. What I find strange in these erasure-reification “wars” is that so many other languages get a pass. And I sort of understand that, languages without a runtime seldom have reflection, or only in some primitive form, and most language on top of a runtime are dynamically typed. So outside of guest languages, Java and C# are unique in this aspect, and Java does use reflection very heavily, where I can imagine that restricted access to the whole type may be a hindrance.
- titzer 4y ago
  It's here: https://static.googleusercontent.com/media/research.google.com/en//pubs/archive/41446.pdf https://static.googleusercontent.com/media/research.google.c... Virgil doesn't have reflection, so not a lot of metadata needed at runtime. It does full monomorphization (like MLTon), so you can't have polymorphic recursion. Of course that could go exponential, but in practice I see something like 20%-30% space overhead. I have a tendency to use polymorphism for really generic datastructures, like lists, vectors, maps, but I use tuples a ton and now I added algebraic datatypes. It's a lot of fun and the compiler generates pretty good code and compiles fast--full optimized bootstrap in < 400ms). Of course everyone worries about exponential code blowup. I have a slightly broken implementation of specialization-up-to-machine-rep, but that's not turned on because of some bugs. I think that's the way I'll go in the future. It is certainly possible to do a type-passing scheme. The built-in interpreter can interpret polymorphic code using dynamic type environments, but can also run monomorphized code. The interpreter is slow.

by titzer 4y ago

kaba0 4y ago

I would be interested in your paper. What I find strange in these erasure-reification “wars” is that so many other languages get a pass. And I sort of understand that, languages without a runtime seldom have reflection, or only in some primitive form, and most language on top of a runtime are dynamically typed. So outside of guest languages, Java and C# are unique in this aspect, and Java does use reflection very heavily, where I can imagine that restricted access to the whole type may be a hindrance.

titzer 4y ago
It's here: https://static.googleusercontent.com/media/research.google.com/en//pubs/archive/41446.pdf https://static.googleusercontent.com/media/research.google.c... Virgil doesn't have reflection, so not a lot of metadata needed at runtime. It does full monomorphization (like MLTon), so you can't have polymorphic recursion. Of course that could go exponential, but in practice I see something like 20%-30% space overhead. I have a tendency to use polymorphism for really generic datastructures, like lists, vectors, maps, but I use tuples a ton and now I added algebraic datatypes. It's a lot of fun and the compiler generates pretty good code and compiles fast--full optimized bootstrap in < 400ms). Of course everyone worries about exponential code blowup. I have a slightly broken implementation of specialization-up-to-machine-rep, but that's not turned on because of some bugs. I think that's the way I'll go in the future. It is certainly possible to do a type-passing scheme. The built-in interpreter can interpret polymorphic code using dynamic type environments, but can also run monomorphized code. The interpreter is slow.