Rust is surprisingly expressive

Re:Rust is surprisingly expressive by com2kid on Saturday December 28, 2013 @07:46PM (#6977457)

One thing I wanted to do awhile back was create an interface that could only be implemented by a class that had already implemented certain other interfaces.

In retrospect, sort of a horrible idea, but I wonder, is there a type system out there expressive enough to allow that behavior?

After a few moments thought I realized why it wouldn't be possible in languages that use a fixed v-table, but it should be possible in languages that use more flexible calling techniques!

Or am I thinking about this too much and this is basically what type classes would buy me?

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Re:Rust is surprisingly expressive by frowaway001 on Saturday December 28, 2013 @08:10PM (#6977590)

> One thing I wanted to do awhile back was create an interface that could only be implemented by a class that had already implemented certain other interfaces.

I think that's easily possible in Scala. I guess one wouldn't even need typeclasses for that.

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Re:Rust is surprisingly expressive by saryant on Saturday December 28, 2013 @10:47PM (#6978235)

This is essentially a Scala "self-type".

  trait InterfaceA

  trait InterfaceB { self: InterfaceA => }

  class A extends InterfaceA // compiles

  class B extends InterfaceB // does not compile

  class B extends InterfaceA with InterfaceB // compiles

"self" isn't a keyword, you can call it whatever you like.

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Re:Rust is surprisingly expressive by com2kid on Saturday December 28, 2013 @11:12PM (#6978332)

Hah, now that is nice.

I forget what convoluted use case I wanted it for. I ended up solving it using composition instead (which is the right solution 99% of the time anyway. :) )

Still though, I love using interfaces as contracts, so I get frequently annoyed at how poorly my tools (limited to C++2003 right now) support doing such!

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