RFR 9: 8138963 : java.lang.Objects new method to default to non-null

[Ivan Gerasimov]

Hi Roger!

In the test, why the 'result' variable is needed?

  242         String result;
  243         errors += (result = Objects.nonNullOf(nullString, 
defString)) == defString ? 0 : 1;
  244         errors += (result = Objects.nonNullOf(nonNullString, 
defString)) == nonNullString ? 0 : 1;
  245         errors += (result = Objects.nonNullOf(nonNullString, 
null)) == nonNullString ? 0 : 1;

I don't see its value being used anywhere.

Sincerely yours,
Ivan

On 08.10.2015 1:24, Roger Riggs wrote:
> Hi,
>
> The original intent was to simplify the filling in of default values 
> (even if null).
> I took Remi's point about  the canonical coalescing operator not 
> always returning non-null
> but the push seems to be in the direction of making sure the result is 
> always non-null.
> I'd rather add a few very useful methods and avoid those with 
> diminishing returns.
>
> I note that nulls are discovered eventually, but doing more aggressive 
> checking is preferred.
> I expect the compiler is able to squeeze out all the extra checks.
>
> In the current context of Objects that the jdk, I read the naming 
> pattern of firstNonNull to imply
> access to some sequential data structure like an array or list; but it 
> doesn't gel with me to apply it to the arg list
> (unless it was varargs).  The pattern of naming us "of"  as being 
> factory producing an object
> from the arguments seems apropos and is concise.
>
> Please consider and comment:
>
>     <T> T nonNullOf(T obj, T defaultObj);
>     <T> T nonNullOf(T, obj, Supplier<T> defaultSupplier);
>
> Details are in the updated webrev:
>      http://cr.openjdk.java.net/~rriggs/webrev-object-non-null/
>
> Regards, Roger
>
>
> On 10/6/2015 6:42 PM, Remi Forax wrote:
>> Null coalescing is a popular operator in several languages [1] and 
>> the usual semantics is nullOrElse and not firstNonNull.
>> In languages like Kotlin or Swift, because there is a distinction 
>> between Object and Object?, it's not a big deal, you can not 
>> de-reference null by error, anyway.
>>
>> Also note that nullOrElseGet, the one that takes a supplier also 
>> exists in Groovy and Kotlin under the name null safe navigation.
>>
>> So even if i prefer the semantics of firstNonNull, i think we should 
>> also include both nullOrElse and nullOrElseGet.
>>
>> regards,
>> Rémi
>>
>> [1] https://en.wikipedia.org/wiki/Null_coalescing_operator
>>
>> -
>
>