[e-lang] Generators for the other Joe-E array types

[Tyler Close]

Hi David,

On Dec 15, 2007 9:30 PM, David Wagner <daw at cs.berkeley.edu> wrote:
> You mentioned that you wanted to eliminate all unsafe casts.  The
> interface above may require casting the return value of snapshot()
> to the appropriate subtype of ConstArray.  For example, consider the
> following usage:
>     Generator<T> g = PowerlessArray.generate(n);
>     ...
>     PowerlessArray<T> a = (PowerlessArray<T>) g.snapshot();
> The last line requires an unchecked cast.  Is that okay?  Would you
> prefer to have the interface be designed to be statically type-safe?
>
> For example, would the following alternative be better?
>     interface Generator<A extends ConstArray<T>,T> {
>         void append(T value);
>         A snapshot();
>     }
> Each Joe-E array type would provide a generate() method that returns
> the appropriate type; e.g., PowerlessArray<T>.generate()'s return type
> would be Generator<PowerlessArray<T>,T>.  That would eliminate the
> need to cast the return value of Generator.snapshot() to the appropriate
> array type.  Does this seem like an improvement?

I was thinking PowerlessArray would provide a public implementation of
the Generator interface and make use of Java's support for covariant
return types in the implementation of the snapshot() method, so...

    public final class
    Generator<T> implements org.joe_e.array.Generator<T> {

        ...
        public PowerlessArray<T>
        snapshot() { return ...; }
    }

Use would then be:

    PowerlessArray.Generator<T> g = PowerlessArray.generate(n);

    PowerlessArray<T> a = g.snapshot();

This is similar to how the ByteArray.Generator class currently works.

--Tyler

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