Model 3 classfile design document

Andrey Breslav andrey.breslav at
Mon Feb 1 05:33:20 UTC 2016

A question about these examples:

   - R(Foo<raw>) = Class["Foo"] or ParameterizedType['L', "Foo", "_"]
   - R(Foo<String>) = Class["Foo"] orParameterizedType['L', "Foo", "_"]
   - R(Foo<int[]>) =ParameterizedType['L', "Foo", ArrayType[1, "I"]]

Apparently, we want to preserve the information about int[], while we don't
care about String. Why? Isn't int[] just a class, like String?

On Fri, Jan 22, 2016 at 7:53 PM Brian Goetz <brian.goetz at> wrote:

> Please find a document here:
> that describes our current thinking for evolving the classfile format to
> clearly and efficiently represent parametric polymorphism.  The early
> concepts of this approach were outlined in my talk at JVMLS last year;
> this represents a refinement of those ideas, and a reasonable "stake in
> the ground" description of what seems the most sensible way to balance
> preserving parametric information in the classfile without imposing
> excessive runtime costs for loading specializations.
> We're working on an updated compiler prototype which people will be able
> to play with soon (along with a formal model.)
> Please ask questions!
> Some things this document does not address yet:
>   - How we deal with types implicit in the bytecodes (aload vs iload)
> and how they get specialized;
>   - How we represent restricted methods in the classfile;
>   - How we represent the wildcard type Foo<any>
> --
Andrey Breslav
Project Lead of Kotlin
The Drive to Develop
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