java11-vavr093-try-workshop

project description

• https://www.vavr.io/vavr-docs/#_try
• https://static.javadoc.io/io.vavr/vavr/0.9.3/io/vavr/control/Try.html
• https://github.com/mtumilowicz/java11-vavr-try
• in the workshop we will try to fix failing tests test/groovy/Workshop
• answers: test/groovy/Answers (same tests as in Workshop but correctly solved)

theory in a nutshell

• Try models a computation that may either result in an exception (Throwable), or return a successfully computed value
• you can think about Try as a pair (Failure, Success) ~ (Throwable, Object) that has either left or right value
• you can think about Try as an object representation of try-catch-finally

  static <T> Try<T> of(CheckedFunction0<? extends T> supplier) {
      Objects.requireNonNull(supplier, "supplier is null");
      try {
          return new Success<>(supplier.apply());
      } catch (Throwable t) {
          return new Failure<>(t);
      }
  }
  

• interface Try<T> extends Value<T>, Serializable
  • interface Value<T> extends Iterable<T>
• two implementations:
  • final class Success<T>
  • final class Failure<T>

conclusions in a nutshell

• conversion Option<T> <-> Try<T>
  • try.toOption()
  • option.toTry()
    • None -> Failure(NoSuchElementException)
• wrapping computations
  • static <T> Try<T> of(CheckedFunction0<? extends T> supplier)
  • note that we could also wrap computations that throws checked exceptions (argument type - CheckedFunction0)
• conversion: List<Try<T>> -> Try<List<T>>
  • Try.sequence(list)
  • if any of the Try is Failure, returns first Failure
• performing side-effects
  • on success:
    • Try<T> andThen(Runnable runnable)

      Objects.requireNonNull(consumer, "consumer is null");
      if (isFailure()) {
          return this;
      } else {
          try {
              consumer.accept(get());
              return this;
          } catch (Throwable t) {
              return new Failure<>(t);
          }
      }
      

    • onSuccess(Consumer<? super T> action)

      Objects.requireNonNull(action, "action is null");
      if (isSuccess()) {
          action.accept(get());
      }
      return this;
      

    • andThen vs onSuccess - exceptions in onSuccess are not wrapped with try
  • on failure:
    • Try<T> onFailure(Consumer<? super Throwable> action)
• mapping with the partial function
  • Try<R> collect(PartialFunction<? super T, ? extends R> partialFunction)
  • if function is not defined for the value - returns Failure(NoSuchElementException)
• map, flatMap on Try<R>
  • Try<U> map(f: R -> U)
  • Try<U> flatMap(f: R -> Try<U>)
• we could filter value (same as Option)
• lazy alternative
  • Try<T> orElse(Supplier<? extends Try<? extends T>> supplier)
• recovery from specific exceptions:
  • Try<T> recover(Class<X> exception, Function<? super X, ? extends T> f)
  • Try<T> recoverWith(Class<X> exception, Function<? super X, Try<? extends T>> f)
• finally block
  • Try<T> andFinally(Runnable runnable)
• try with resources
  • Try.withResources(CheckedFunction0<? extends T1> t1Supplier)
• mapping exception
  • Try<T> mapFailure(Match.Case<? extends Throwable, ? extends Throwable>... cases)