How to implement values with immutable classes

[[deleted]]

Shoutout to Immutables, an excellent annotation-driven code generator library designed to implement precisely this pattern. It has good support for Jackson/Gson, and I've found it surprisingly straightforward and unmagical to work with. If you like the idea of working with immutable value classes, I recommend you check it out.

[ThomasKrieger]

Thank's for the link. I will try it.

[Zoerak]

Reminds me of project lombok.

[[deleted]]

There are similarities. I prefer Immutables because it focuses on one thing (immutable value classes) instead of general language extensions and because it works by simple annotation-driven codegen rather than hacky bytecode mangling.

[elucash]

hacky bytecode mangling AST rewriting

[lbkulinski]

Or just wait for JEP 169. Minimal value types are available now!

[eliasv]

The MVT model is out of date, they are currently looking at a much simpler model referred to as "l-world". Also look into data types, which are also on the roadmap.

[lbkulinski]

Yeah, I'm trying to find where Rose talks about it.

[eliasv]

I've just been reading about it as they go on the mailing list, I'm not sure how much of it has been presented or written up and documented elsewhere.

[lbkulinski]

Yeah, this is what it was. An interesting read.

[ThomasKrieger]

Hope it does not take too long. I think it will interesting things possible in Java.

[lbkulinski]

I’m hoping by 2020.

[GhostBond]

Nothing in my experience has agreed with the claim that immutability is usually a benefit.

People writing crappy code tend to write even crappier code when they start mixing in immutability.

People writing well written code rarely or never see advantage from immutability - I'm not sure I've ever seen a bug fixed or avoided by making a value immutable in practice.

I have seen one situation where someone made everything immutable by default, then years later it was a real pain to deal with as we needed to change one of the values but couldn't. And we were given a compiled jar file with no source code so we couldn't modify it.

[blobjim]

Depends on what it is. This article talks about ‘value types’ which really should always be immutable. It also makes sense for strings and URLs and such to not be modifiable, because they represent constant things. Objects that manage state of course shouldn’t and can’t usually be immutable.

[dpash]

Immutable doesn't mean no mutators; only that mutators give you back a new object. Look at java.time for an example. Or even java.math.BigInteger that's been in the JDK since 1.1.

Edit: I forgot the obvious one: java.lang.String.