EDN List, Vector types indistinguishable due to common RandomAccess interface about edn-java HOT 5 CLOSED

Yes, that's a bug, though what this commit says is true: ArrayLists are indeed better than LinkedLists in that they use less memory and are faster to iterate.

Hanging the whole List/Vector distinction on the presence or absence of the RandomAccess marker interface is a bit of a hack. I'm not very happy with it and find myself wishing for Clojure-like meta-data. This strategy also presents a problem for edn-java-guava, since Guava's immutable list classes all implement RandomAccess.

Two alternatives that might be better than reverting the commit above to return java.util.LinkedList implementations:

1. Return a java.util.List which merely wraps a java.util.ArrayList, but does not itself implement RandomAccess.
2. Return a custom implementation of java.util.List which chunks by actually being a list of fixed-size chunks under the hood.

The downside of doing nothing is what this issue is about. The downside of 1 is the additional indirection introduced for delegation. (Though Iteration can be direct.) The downside of 2 is the implementation effort and probability of introducing bugs.

I'm thinking the first approach sounds like it's worth it; the second is unlikely to be worth it.

What do you think?

from edn-java.

See https://github.com/bpsm/edn-java/commits/feature/issue32

from edn-java.

Why not just do a lightweight custom implementation of ArrayList? I don't think chunking actually buys us anything here, indeed it's probably going to add more overhead than an extra layer of indirection.

If you are interested in that approach, I think I've got some old code hanging around that would get us 80% there....

from edn-java.

Ben,

I agree with your rationale. LinkedList has poor performance characteristics and option 2 seems like asking for trouble. Your provided solution is quite clean.

On the issue of this handling Guava collections, I wonder if the code to determine List or Vector should be separated out into an interface. This would be something like:

interface SequenceTypeSelector {
    boolean isVector(Object o);
}

The selector could be attached to the ProtocolBuilder for the Printer (with a default implementation provided of course). Extending SequenceTypeSelector would allow custom dispatch for types, allowing the simple if-else select on java.util.RandomAccess, or a Map lookup for more complex type hierarchies.

from edn-java.

I'm going to release https://github.com/bpsm/edn-java/commits/feature/issue32 as 0.4.2. Making distinguishing between list and vector pluggable as been moved to issue #33 and tentatively assigned to milestone 0.5.0.

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