Java Future Optional Monad

FutureOptional.java

package com.github.vjames19.functional;

import lombok.RequiredArgsConstructor;

import java.util.Optional;
import java.util.concurrent.CompletableFuture;
import java.util.function.Function;

import static java.util.concurrent.CompletableFuture.completedFuture;

@RequiredArgsConstructor
public class FutureOptional<T> {

    private static final FutureOptional EMPTY = futureOptional(Optional.empty());

    private final CompletableFuture<Optional<T>> future;

    public static <T> FutureOptional<T> futureOptional(Optional<T> optional) {
        return new FutureOptional<>(completedFuture(optional));
    }

    public static <T> FutureOptional<T> futureOptionalPresent(CompletableFuture<T> future) {
        return new FutureOptional<>(future.thenApply(Optional::ofNullable));
    }

    public static <T> FutureOptional<T> futureOptional(CompletableFuture<Optional<T>> future) {
        return new FutureOptional<>(future);
    }

    @SuppressWarnings("unchecked")
    public static <T> FutureOptional<T> empty() {
        return (FutureOptional<T>) EMPTY;
    }

    public <R> FutureOptional<R> map(Function<T, R> f) {
        return futureOptional(future.thenApply(optional -> optional.map(f)));
    }

    public <R> FutureOptional<R> flatMap(Function<T, FutureOptional<R>> f) {
        final CompletableFuture<Optional<R>> fu = future.thenCompose(optional -> optional
                .map(value -> f.apply(value).future)
                .orElse(completedFuture(Optional.empty())));
        return futureOptional(fu);
    }

    public CompletableFuture<Optional<T>> future() {
        return future;
    }
}