alexec/java-case

I really like mixing Scala case classes and matchers. They make for easy to read code. I wondered if we could do something similar in pure Java?

Java 8 lambdas allow us to start writing code that feels like new language constructs. It's great for DSLs for example.

How about this?

int x = match(
        new MyValueObject1(0),
        when(equalTo(new MyValueObject1(0)), () -> 0),
        when(not(new MyValueObject1(0)), () -> 1)
);

The match method here takes two things, and object and a Branch, and tries each branch in turn to see if it matches, if so, return the branch's value:

public static <T,U extends T,O> O match(U o, Branch<T,O>... branches) {
    for (Branch<T,O> b : branches) {
        if (b.matcher.matches(o)) {
            return b.block.get();
        }
    }
    throw new IllegalStateException("no matching branch");
}

A Branch is a simple tuple of a Hamcrest Matcher and a Java 8 Supplier.