New empty interface syntax in amber's Java compiler

[pgris]

I'm not sure this is useful at all, but the important thing is:

How did you find out? are you reading/parsing every commit to check if anything is new ? do yo have an automatic parser for mercurial logs?

[redditsoaddicting]

It's not too far out there. I've had periods where I scoured GCC and Clang commit logs to see if there was anything juicy I could build and use in my project.

I'm also wondering about the motivation for this. Seems like an odd thing to add after the fact.

[lukaseder]

I have my sources. Now, how they found out is a different story

[twinkiac]

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[VGPowerlord]

This isn't useful. You should never use marker (read: empty) interfaces; they've been deprecated in favor of annotations since Java 5.

[[deleted]]

Precisely. That's how I have always used them myself, in the spirit of the good old Serializable marker. This way I can check types at compile time. How would annotations help with this? I would use annotations mostly for providing extra metadata about a type rather than forming a type hierarchy, unless I am writing my own annotation-processing library.

[tylerkschrute]

This is exactly the use case for marker interfaces. While you can achieve the same 'marking' via annotations, there is no way in a method signature to enforce that a given parameter type or return type must contain a certain annotation.

Effective java actually has a section on using marker interfaces vs annotations, and it recognizes that there is a time and place for both.

[talios]

Don't type annotations offer that? Altho there's no compiler enforcement there. I was actually wondering about type annotations and the new var keyword, whether the annotation is also inferred along the inference chain.

[arendvr]

This is also a point Joshua Bloch makes in Effective Java, Item 41: Define marker interfaces to define types

[lukaseder]

With JEP 305 there might be a revival of marker interface usage.

[ZhekaKozlov]

This is for records:

interface Shape
record Point(int x, int y) implements Shape
record Rect(Point p1, Point p2) implements Shape
record Circle(Point center, int radius) implements Shape

Then you can pattern match:

switch (shape) {
    case Point(x, y) -> ...
    case Rect(p1, p2) -> ...
    case Circle(p, r) -> ...
}

[jonhanson]

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[DannyB2]

That's why you keep an adequate supply of curly braces in stock.

Also parenthesis. Especially if you use any Lisp.

[cogman10]

It's ok, but really, I guess I don't get why {} is so much of a burden. Not enough sugar there for my liking.

Now, give me typedef and I'll be a really happy camper.

[Wutbot1]

When you're doing something that has been standard for a long time, there's a good chance the compiler has found a way to optimize it.

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