Sun to Add Variance to Java in 1.5?

Ahe writes "I have been working on a joint project between Sun Microsystems, The University of Aarhus, and The Alexandra Institute. As you might know, Sun has for long been commited to adding generics to Java. Our project was to extend this with variance annotations for more flexible typing of parameterized classes and arrays. Recently Sun has released the project result as a new prototype with variance. If you like variance, please vote for this bug."

Comments

Definitely a bug!

[Twylite]

Generics are at best a trade-off: compile-time type safety in exchange for less readable code. A poor trade-off at best.

Java never has and never will suffer the catastrophic consequences of type casting that C++ can. Type casts are all subject to runtime checks, so that the worst possible result is that an exception will be thrown. Where C++ has no safety without generics, Java has runtime safety.

As for readability, C++ has two major benefits over Java: a preprocessor and typedefs. Without at least one of these features, generics make code almost unreadable. Little wonder that developers new to C++ are very cautious about getting involved with generics, or that old hands know how long it has taken for the STL to become mostly stable (I say mostly, because using STL with threads in cross-platform development is a recipe for disaster).

Java is starting to look very much like something designed by a committee. A pity, because at its core it is still a good thing.

Re:Definitely a bug!

[iabervon]

The only way in which generics make code less readable is the awful angle brackets; otherwise it's a bit more verbose but no less clear, and verbosity has been an aspect of Java from the beginning.

In C++, the reason people are scared of templates is that they're actually quite complicated, with historical stability problems and continuing unexpected behavior. Java only supports the more obvious cases.

Java has been designed by committee from the start, but it's always been an extremely conservative committee; they only include features that a lot of people agree on and of which there are working implementations which have been tested enough to verify that the feature behaves as expected. They're also perfectly happy to not add a feature if it would cause problems, or to send it back for more discussion. C++ has had a lot of problems due to idealism and abstract discussion.

It is significant that, in working on generics and variance, they've gone through the entire Collection library and considered how it should be modified to support all existing code while giving benefits to new code.

Insightful? Come on!

[hummassa]

Ok. This is my first real drooling mad rant. Forgive me.

[rant]
about C++ casting (covariant model of generics): old-style casting was never of real use. use new_style_casts(x) and you have run-time checking, too. other stuff said about this is C++ ignorance.
[/rant]

ohboy, I had to get it off my chest.