try-with-resources and null resource

[Rémi Forax]

  Le 28/01/2011 07:38, David Holmes a écrit :
> Tim Peierls said the following on 01/28/11 00:47:
>> I don't know about C#, but I like the formulation that can be sloppily
>> summarized as "t-w-r calls close on non-null resources".
> So to summarize there are three potential candidates for:
>
> try (Resource r = getResource() {
>     // stuff here
> }
>
> I'm ignoring the suppressed exception aspects for simplicity:
>
> a) Simple transformation into try-finally (current implemented semantics)
>
>     Resource r = getResource();
>     try {
>       // stuff here
>     }
>     finally {
>       r.close();
>     }
>
> b) Transformation into try-finally with explicit null-check on entry
>
>     Resource r = getResource();
>     Objects.requireNonNull(r); // heh heh - couldn't resist!
>     try {
>       // stuff here
>     }
>     finally {
>       r.close();
>     }
>
> c) Simple transformation into try-finally but only close a non-null resource
>
>     Resource r = getResource();
>     try {
>       // stuff here
>     }
>     finally {
>       if (r != null)
>         r.close();
>     }
>
>
> Option (a) is, perhaps, the most consistent with preserving the
> behaviour of current code that would be modified to use the new
> construct. This construct will be taught by analogy as it is the only
> effective way to explain things "try-with-resources behaves as-if you
> had written ....". That said I think existing code would have an
> explicit null-check to avoid the try-finally in the null case. And I
> think it is potentially risky to execute the try block only to have NPE
> thrown later.
>
> Option (c) seems appealing in some sense because there's no NPE's at all
> if you don't use "r", but I think that appeal is superficial. To me the
> fundamental question to ask is: what is try-with-resources for? And I
> believe the answer to that is to initialize, use and then clean-up an
> AutoCloseable object. So to me using try-with-resource on a resource
> that might be null is simply a mis-use of try-with-resources: if it can
> be null you can't autoclose it, so trying to is a programming error and
> programming errors should be detected and reported as early as possible.
> So to me option (b) is the preferred semantics for this new construct.
>
> David Holmes

+1 :)

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