This is my humble attempt at a practical Result type for Java.
It is based heavily on the Result type from Rust and care has
been taken to make sure it can be propagated in the event of
failure.
public final class Example {
public static void main(String[] args) throws Throwable {
// Happy to re-throw? Go for it!
System.out.println(getInteger().map(i -> i + 1).getOrThrow());
// Want to do error checking? No problem!
Result<String> result = Result.from(App::woot).map(String::toUpperCase);
if (result.isError()) {
System.err.println("Oh no!");
} else {
System.out.println("Result: " + result.get());
}
// Want to add more info to errors? We got you.
String username = Result.from(App::fetchUsername)
.wrapError(IllegalArgumentException::new, "unable to find user")
.getOrThrow();
}
public static String fetchUsername() throws IOException {
return mayThrow(); // pretend there's business logic here
}
public static Result<Integer> getInteger() {
return getString().map(Integer::valueOf);
}
public static Result<String> getString() {
if (ThreadLocalRandom.current().nextBoolean()) {
return Result.success("10");
} else {
return Result.fail(new IllegalStateException("Ruh roh"));
}
}
public static String mayThrow() throws IOException {
if (ThreadLocalRandom.current().nextBoolean()) {
return "Success!";
} else {
throw new IOException("Rats!");
}
}
}