spencerwi / either.java Goto Github PK

public abstract class Try<A> extends Either<Throwable, A> but then I don't know how to implement Success and Failure.

In the changelog my username is given as hamishwilson instead of the correct hamishlawson

Hello,
I was very happy you made the effort to create this library.
Also I like how you added the Result-approach.

I am missing a run method for the Result class.
There is one in the Either so I will change my current usage of the library to the Either-Approach.

map and FlatMap have basically the same Type Signature apart from Exception Handling, which is wrong.

public abstract <T> Result<T> map(Function<R,T> transformValue);
public abstract <T> Result<T> flatMap(ExceptionThrowingFunction<R,T> transformValue);

Compared to flatMap on Scalas Try (or pretty much any other Class with flatMap in any functional Language):

 flatMap[U](f: (T) ⇒ Try[U]): Try[U] 

I'd like to have a "real" flatMap Function. Catching Exceptions and translating to Result should be done by both, map and flatMap.

What's the reason for using 2 value pointers per element instead of one:

public abstract class Either<L, R> {
    protected L leftValue;
    protected R rightValue;

It seems like every indirection via Either will double the required space for the pointers. Shy of a union type, you could have used java.lang.Object and cast it dynamically to L or R.

Next scenario from the readme fails, however it's expected that it'll wrap exceptions from chained methods

@Test
public void map() {
    Result<?> result = Result.attempt(() -> someOperationThatMightFailOrReturnA())
            .map(a -> someOtherOperationThatMightFailOReturnB(a))
            .map(b -> someThirdOperationThatMightFailOrReturnC(b));
    Assert.assertTrue(result.isErr());
}

private Object someThirdOperationThatMightFailOrReturnC(Object b) {
    return Objects.requireNonNull(b);
}

private Object someOtherOperationThatMightFailOReturnB(Object a) {
    return Objects.requireNonNull(a);
}

private Object someOperationThatMightFailOrReturnA() {
    return null;
}

java.lang.NullPointerException
	at java.util.Objects.requireNonNull(Objects.java:203)
	at com.spencerwi.either.ResultMapTest.someOtherOperationThatMightFailOReturnB(ResultMapTest.java:27)
	at com.spencerwi.either.ResultMapTest.lambda$map$1(ResultMapTest.java:16)
	at com.spencerwi.either.Result$Ok.map(Result.java:108)

Hi @spencerwi,

I was wondering if you can think about and then add a license for this library (which is very nice and simple that's why I like it!).

Thank you very much!