Result.java

package com.accorlight;

import java.util.function.Function;

public final class Result<R, E> {
	final R value;
	final E error;

	public static class ResultException extends RuntimeException {
		public ResultException(final String message) {
			super(message);
		}
	}

	private Result(final R value, final E error) {
		this.value = value;
		this.error = error;
	}

	private final boolean isOk() {
		return this.error == null;
	}

	private final boolean isError() {
		return !isOk();
	}

	public final R get() {
		if (isOk()) {
			return value;
		}
		throw new ResultException("Expected an ok result but got an error");
	}

	public final E getError() {
		if (isError()) {
			return error;
		}
		throw new ResultException("Expected an error but got an ok result");
	}

	public static final <R, E> Result<R, E> ok(R value) {
		return new Result<>(value, null);
	}

	public static final <R, E> Result<R, E> error(E error) {
		return new Result<>(null, error);
	}

	public final <T> Result<T, E> map(Function<R, T> f) {
		return this.isOk() ? ok(f.apply(this.value)) : error(this.error);
	}

	public final <T> Result<T, E> bind(Function<R, Result<T, E>> f) {
		return this.isOk() ? f.apply(this.value) : error(this.error);
	}

	public final <T> Result<R, T> mapError(Function<E, T> f) {
		return this.isError() ? error(f.apply(this.error)) : ok(this.value);
	}

	public static final <T> T merge(Result<T, T> r) {
		return r.isOk() ? r.value : r.error;
	}
}