Optional.orElseChain ?

[Steven Schlansker]

On Apr 17, 2015, at 2:37 PM, Remi Forax <forax at univ-mlv.fr> wrote:
> As you can see the code is not bad but the code of chain() could be simplified
> if there was a way on Optional to call a Supplier of Optional if an Optional is empty.
> Currently, orElse() takes a value, orElseGet takes a lambda that will return a value
> and there is no method that takes a lambda and return an Optional
> (like flatMap but but with a supplier that will be called if the Optional is empty).
> 
> If we add the method orElseChain(Supplier<? extends Optional<T>> supplier)
> perhaps with a better name ?, then the code of chain is better:
> 
>  public default TypeProvider chain(TypeProvider provider) {
>    return name -> loadType(name).orElseChain(() -> provider.loadType(name));
>  }
> 
> Am i the only one to think that this method is missing ?

We actually ran into the exact same problem, and wrote the following helper method:

public static <X> Optional<X> unlessOpt(@Nonnull Optional<X> first, Supplier<Optional<X>> second) {
    return first.isPresent() ? first : second.get();
}

I don't think it's precisely the same as your solution, but it definitely indicates a missing method.