Better type inference for Scala: send us your problematic cases!

Language Design
88

Re: the usage of val foo = new Foo { val x = 3 }:

I think rewriting object foo extends Foo { val x = 3 } is hard for us Chisel people for multiple reasons:

  • What we actually do is val foo = func(new Foo { val x = 3 }) where func is def func[T](in: T): T. Writing func(object Foo { ... }) is not legal.
  • This pattern is in our hello world. It appears in almost every Chisel user’s code.
    Searching public github repos shows > 4k usages.
  • This is a backwards compatibility problem for all of our users, and it seems onerous to make a code-rewriter and require everyone to use it.
  • More generally, this pattern is useful and important for Chisel’s goals as a hardware DSL. From our experience, structural typing is a very familiar paradigm for Verilog/VHDL users- we try to add more safety while still giving a familiar look and feel.