Honestly IMO Java is in a very good spot right now. Mature technology, maybe a bit "unsexy", but rock-solid and future-proof.
There are still pain points, but the language is leaps and bounds better than the Java 1.6 days.
There are still pain points, but the language is leaps and bounds better than the Java 1.6 days.
The springification is what I mean by it being externalized and you generally don't see that in C, no. The pre-processor might be sort of the same thing but you generally don't bootstrap the entire thing using it.
But this is absolutely domain-specific, Java the language is indifferent to exposing a library that will handle incoming request and dispatch them based on some library logic, or creating a “traditional” program for the litany of other domains where java is used st.
If you'd chosen languages that permit abstractions in a real and usable sense, then you would not need this. In fact: with _one_ exception, I've never had a container in any Haskell, Scala or F# project ever. Do you think we ever needed one?
And this is my point: those other languages have seen _tons_ of development in the "abstraction arena" with (internal) DSL:s and super powerful frameworks for making powerful DSL:s. Java has had none of this because these concerns har all (poorly) handled at the container level.
The tacked on "functional stuff" is for sure cool coming from a Java backround, but they're pretty much useless.
This "containerizing" is very unique to Java -- I've never seen anything like it in the other various languages I've used. I won't even mention the total disaster of JavaEE containers.
My point, though, is not to throw up all over Java but rather to quibble with the statement that Java has somehow evolved since then. It really hasn't!
https://www.destroyallsoftware.com/screencasts/catalog/funct...
Basically you have business domain objects that have value semantics and are immutable. You have functions that manipulate these objects. This makes the business domain unit-testable. Then on the edge of the application you have imperative code that manipulates databases, serves requests, etc. It’s like Haskell but as a design pattern rather than a language.
In the JVM world, Scala and Clojure communities are adopting this approach.
It is essentially straight forward to do. You look at a bunch of code in a module and determine which parts do these kinds of things:
- data integrity, validation
- parsing, transformation between formats
- domain logic, decision making
- algorithms and data structures
This is your functional core. Note it doesn't matter too much if you have local mutations as long as they don't leak out. What you want to achieve is to have an interface where you can ask questions and you get the same answer for a particular question. This is certainly more productive if your language affords you with functional constructs, but its not strictly necessary to get the benefits.
You code these parts in a way that they are data in, data out essentially. This leads to super easy and reliable unit/example tests and generative tests. And this part becomes very simple and easy to reason about.
Secondly you have the part of your code that actually _does_ stuff, affecting your environment in some way.
- basically any kind of I/O
- cross cutting concerns between other side effecting modules and services (think DI and such)
- error handling, error reporting and logging
- caching, throttling, filtering etc.
That's your imperative shell (I just call them modules). This part you write in an imperative/procedural style and you call the functional core parts from here, never the other way around. You coordinate effects so to speak.
It is clear that you test these with integration tests, where you need to setup specific program state (or use mocks, but I try to avoid that) in order to find different code paths. This is harder to test properly but at the same time you also get to see everything that actually happens in condensed form.
The degree to which you extract "pure" logic from your imperative shell is actually quite flexible. You can go as far as defining purely functional FSMs to extract much of the control for example. I think it really depends on code size and complexity as well as performance implications. The cool thing is that you can be quite pragmatic and iterative about it.
Of course you can't have the pure/impure distinction enforced, but nothing that isn't a purely functional language is going to give you that.
The only really dumb limitation is that you can't have freestanding functions, but that's aesthetics more than substance.