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*De: *"Roger Riggs" <roger.ri...@oracle.com>
*À: *fo...@univ-mlv.fr
*Cc: *"core-libs-dev" <core-libs-dev@openjdk.java.net>
*Envoyé: *Jeudi 8 Octobre 2015 21:09:26
*Objet: *Re: RFR 9: 8138963 : java.lang.Objects new method to
default to non-null
So for you, method overloading is a mis-feature of the language
because it inhibits readability.
Though I might argue, that the magic type inference is the real
culprit.
In most coding cases, the types of the arguments are visible
and/or via syntax and naming.
Thanks, Roger
I don't really like overloading mostly because the rules that govern
overloading are too complex. When you introduce a new feature like auto-boxing
or lambda auto-conversion in the language, you can not say that a call is
ambiguous with the new rules because it will break backward compatibility, so
you end up with weird overloading rules that you can only understand in the
light of the Java history.
Anyway, in this case the problem is not just overloading, it is the mix of
overloading and type inference as you said.
I vaguely remember that we, the lambda EG, discuss about javac emitting a
warning for cases like this one.
regards,
Rémi
On 10/8/2015 2:37 PM, fo...@univ-mlv.fr wrote:
Hi Roger,
my point was that for me, all theses forms are ambiguous thus
not readable.
*De: *"Roger Riggs" <roger.ri...@oracle.com>
*À: *"Remi Forax" <fo...@univ-mlv.fr>
*Cc: *"core-libs-dev" <core-libs-dev@openjdk.java.net>
*Envoyé: *Jeudi 8 Octobre 2015 16:44:54
*Objet: *Re: RFR 9: 8138963 : java.lang.Objects new method
to default to non-null
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.
I'm not sure you can say this is the expected result. Why the
compiler doesn't call <T> T nonNullOf(T, T) and return () ->
null as Supplier ?
In the second case, the () -> "" is a supplier<String> not
a Supplier<Supplier<String>>.
The compiler correctly produced a error.
Why the compiler doesn't select the method <T> T nonNullOf(T,
T) instead, this version compiles !
and if you want more weirdness, what about ?
Object o = Objects.nonNullOf"foo", null);
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>>.
maybe "nonNullOfGet" is a bad name, my point is that when you
have several overloads like this, the result is not easy to
predict (I suppose that people don't know by heart the chapter
15.12.2 of the JLS).
[...]
Thanks, Roger
regards,
Rémi
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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