Hi Remi,
On 10/8/2015 4:49 AM, Remi Forax wrote:
Hi Roger,
using overloads here seems to be a bad idea,
as a nice puzzler, what does the compiler do for these two lines of code
Supplier<String> supplier = Objects.nonNullOf(null, () -> null);
Supplier<String> supplier2 = Objects.nonNullOf(null, () -> "");
The first form compiled and threw the expected NPE at runtime.
In the second case, the () -> "" is a supplier<String> not a
Supplier<Supplier<String>>.
The compiler correctly produced a error.
I don't think the method name will help the developer much and just
makes the name longer
for everyone else who is not producing a Supplier<Supplier<T>>.
The other issue is that defaultSupplier should allow covariant Supplier,
the signature should be:
<T> T nonNullOfGet(T obj, Supplier<? extends T> defaultSupplier)
Right, as Chris pointed out also.
Thanks, Roger
otherwise apart form the remark of Stephen, the code is Ok.
cheers,
Rémi
----- Mail original -----
De: "Roger Riggs" <roger.ri...@oracle.com>
À: "core-libs-dev" <core-libs-dev@openjdk.java.net>
Envoyé: Jeudi 8 Octobre 2015 00:24:26
Objet: Re: RFR 9: 8138963 : java.lang.Objects new method to default to non-null
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
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