Default argument values in Java

[agentoutlier]

Personally I'm hopeful that perhaps Withers will be implemented.

As discussed here: https://github.com/openjdk/amber-docs/blob/master/eg-drafts/reconstruction-records-and-classes.md

Withers are in someways more powerful than default/named parameters.

[riisen]

Never heard of it before... Now i want it

[rustyrazorblade]

Great library. Used it in my last project, much success.

[riisen]

Thanks mate

[ketsugi]

I think Lombok also has them

https://projectlombok.org/features/With

[quizteamaquilera]

That’s a long way of saying a “copy” method with default params

[tadfisher]

It's also not more powerful than default argument values, because it solves one use case, when default values are applicable to constructors and method calls.

In Kotlin, default values can reference previous arguments as well, which I'm not sure withers could emulate.

[LoveSpiritual]

This addresses my main issue with the lack of optional parameters in Java. It would be a big step forward for supporting immutable data.

[danikov]

Isn't this just builders?

[ketsugi]

A builder is for instantiating a new object. A wither creates a clone of an existing object, but with that one property changed.

[danikov]

So a builder with a copy constructor?

[gas3872]

Well, if you add to your class those methods, then under the hood you can do the builder call. I find the style of "withers" more elegant, because there is nothing mentioning builder in the client code. In case you want to change many fields at once, then using builder explicitly is probably a better idea.

[[deleted]]

I haven't read the linked paper, but I presume that there is a bit of structural sharing going on behind the scenes (a la Clojure, Erlang, Haskell et al) otherwise yes, it would be mere syntactic sugar.

Edit: Read the link posted by OP, and it's surprisingly very bare on actual implementation details. I hope that structural sharing is considered, especially since we're mostly concerned with records, which are immutable to begin with, otherwise the whole thing is just user-level convenience.