Re: RFR: 8015317: Optional.filter, map, and flatMap
I did supply a test that you can use to try it.
What we are talking about is whether type BoxParent is substitutable by
BoxChild in the contravariant position. Intuitively we think we only need
Box? extends Parent because we only care about the type parameter, but
the type – as you point out – is actually different. BoxParent is not
inherited by BoxChild.
Specifically, if we have a consuming Box, and we replace it with a Box of a
more specific type parameter, we could attempt feed the more general type
into it, ie. a BoxChild isn't going to appreciate having Parent fed to
it. This is why covariance and mutable containers don't mix well, and why
Java's covariant arrays are problematic.
In this situation we have an immutable container, and we can substitute the
type of our container with one of a more specific type, as it will only
ever supply a value – and a value of Child will suffice as a Parent. So,
for this case we need a Box that is substitutable, and therefore we need to
add the covariance to our box.
? extends Box is simply adding covariance to our Box type.
For a much better explanation than I can give about this, see this
excellent post describing generics in Scala, which – apart from have
declaration-site variance and using [A] in place of A – generally follow
the same pattern:
http://termsandtruthconditions.herokuapp.com/blog/2012/12/29/covariance-and-contravariance-in-scala/
cheers,
jed.
On 14 July 2013 04:49, Henry Jen henry@oracle.com wrote:
I think the type you talking about here is Optional? extends U instead
of ? extends OptionalU.
IIRC, Optional? extends U is not a subtype of OptionalU, just like any
other Collection class. ListChild is not a ListParent.
Cheers,
Henry
On Jul 13, 2013, at 3:15 AM, Jed Wesley-Smith j...@wesleysmith.io wrote:
The ? extends Optional is unnecessary in flatMap as Optional is final.
interestingly enough, it actually is.
try the following test:
class OptionalTest {
class Parent {};
class Child extends Parent {};
@Test public void covariantReturn() {
OptionalParent some = some(new Parent());
FunctionParent, OptionalChild f = new FunctionParent,
OptionalChild() {
@Override public OptionalChild apply(Parent p) {
return some(new Child());
}
};
OptionalParent mapped = some.Parent flatMap(f);
assertThat(mapped.get(), notNullValue());
}
}
adapted from the fugue test suite:
https://bitbucket.org/atlassian/fugue/src/96a65067fb7aaf1edae1bffa07167a5865cbebec/src/test/java/com/atlassian/fugue/OptionTest.java#cl-155
The point to remember is that OptionalChild is a type and as such is
actually a subtype of OptionalParent – and therefore requires a
covariant return.
cheers,
jed.
On 13 July 2013 04:15, Mike Duigou mike.dui...@oracle.com wrote:
The ? extends Optional is unnecessary in flatMap as Optional is final.
Otherwise this looks good.
Mike
On Jul 5 2013, at 14:37 , Henry Jen wrote:
Hi,
Please review the webrev at
http://cr.openjdk.java.net/~henryjen/ccc/8015317.0/webrev/
Which adds following method to Optional,
public static T OptionalT ofNullable(T value) {}
public OptionalT filter(Predicate? super T predicate) {}
publicU OptionalU map(Function? super T, ? extends U mapper) {}
publicU OptionalU flatMap(Function? super T, ? extends OptionalU
mapper) {}
Also included is some cleanup on javadoc.
Cheers,
Henry
Re: RFR: 8015317: Optional.filter, map, and flatMap
I'm not entirely sure that is a problem, have a look at the following:
https://gist.github.com/jedws/5993596#file-variancetest-java
it is only the one with a covariance annotation on the parameter that fails…
On 15 July 2013 12:52, Zhong Yu zhong.j...@gmail.com wrote:
Another example of possible missing a wildcard
http://gee.cs.oswego.edu/dl/jsr166/dist/docs/java/util/concurrent/CompletionStage.html#thenCompose%28java.util.function.Function%29
thenCompose(Function? super T,? extends CompletionStageU fn)
should be
thenCompose(Function? super T,? extends CompletionStage? extends U
fn)
The problem is probably wide spread, and we need a tool to find these
mistakes.
Zhong Yu
On Sun, Jul 14, 2013 at 8:04 AM, Jed Wesley-Smith j...@wesleysmith.io
wrote:
(accidentally didn't post to the list)
You probably know that the example provided is not completed ported to
work with our Optional implementation,
It should be, for the example I wrote an Optional that is final and
should
be otherwise identical. It should certainly be fairly easy for any
committer to try. If you can make it work without the ? extends Optional
I'd love an explanation of how.
and fugue works around the type system with Option as abstract class.
As I've tried to explain, this isn't about the implementation of the
container class, but how covariance works with a parameterised class.
We originally had the non-, but in a discussion with Brian he alerted us
to
the fact that the signature was wrong. We hastily fixed it:
https://bitbucket.org/atlassian/fugue/commits/9eca663326a5baeb8f23974732ec585d5627a05c
To further demonstrate, I give you a minimal example of a final Optional
implementation that does not compile for this test:
https://gist.github.com/jedws/5993596#file-gistfile1-java-L57
cheers,
jed.
On 14 July 2013 15:02, Henry Jen henry@oracle.com wrote:
I think I understand what you are saying. However, unless we make
Optional not final, the extends part just doesn't matter.
You probably know that the example provided is not completed ported to
work with our Optional implementation, and fugue works around the type
system with Option as abstract class.
Cheers,
Henry
On Jul 13, 2013, at 4:35 PM, Jed Wesley-Smith j...@wesleysmith.io
j...@wesleysmith.iowrote:
I did supply a test that you can use to try it.
What we are talking about is whether type BoxParent is substitutable
by BoxChild in the contravariant position. Intuitively we think we
only
need Box? extends Parent because we only care about the type
parameter,
but the type – as you point out – is actually different. BoxParent is
not
inherited by BoxChild.
Specifically, if we have a consuming Box, and we replace it with a Box
of a more specific type parameter, we could attempt feed the more
general
type into it, ie. a BoxChild isn't going to appreciate having Parent
fed
to it. This is why covariance and mutable containers don't mix well, and
why Java's covariant arrays are problematic.
In this situation we have an immutable container, and we can substitute
the type of our container with one of a more specific type, as it will
only
ever supply a value – and a value of Child will suffice as a Parent. So,
for this case we need a Box that is substitutable, and therefore we
need to
add the covariance to our box.
? extends Box is simply adding covariance to our Box type.
For a much better explanation than I can give about this, see this
excellent post describing generics in Scala, which – apart from have
declaration-site variance and using [A] in place of A – generally
follow
the same pattern:
http://termsandtruthconditions.herokuapp.com/blog/2012/12/29/covariance-and-contravariance-in-scala/
cheers,
jed.
On 14 July 2013 04:49, Henry Jen henry@oracle.com wrote:
I think the type you talking about here is Optional? extends U
instead
of ? extends OptionalU.
IIRC, Optional? extends U is not a subtype of OptionalU, just like
any other Collection class. ListChild is not a ListParent.
Cheers,
Henry
On Jul 13, 2013, at 3:15 AM, Jed Wesley-Smith j...@wesleysmith.io
wrote:
The ? extends Optional is unnecessary in flatMap as Optional is
final.
interestingly enough, it actually is.
try the following test:
class OptionalTest {
class Parent {};
class Child extends Parent {};
@Test public void covariantReturn() {
OptionalParent some = some(new Parent());
FunctionParent, OptionalChild f = new FunctionParent,
OptionalChild() {
@Override public OptionalChild apply(Parent p) {
return some(new Child());
}
};
OptionalParent mapped = some.Parent flatMap(f);
assertThat(mapped.get(), notNullValue());
}
}
adapted from the fugue test suite:
https://bitbucket.org/atlassian
Re: RFR: 8015317: Optional.filter, map, and flatMap
(accidentally didn't post to the list)
You probably know that the example provided is not completed ported to
work with our Optional implementation,
It should be, for the example I wrote an Optional that is final and should
be otherwise identical. It should certainly be fairly easy for any
committer to try. If you can make it work without the ? extends Optional
I'd love an explanation of how.
and fugue works around the type system with Option as abstract class.
As I've tried to explain, this isn't about the implementation of the
container class, but how covariance works with a parameterised class.
We originally had the non-, but in a discussion with Brian he alerted us to
the fact that the signature was wrong. We hastily fixed it:
https://bitbucket.org/atlassian/fugue/commits/9eca663326a5baeb8f23974732ec585d5627a05c
To further demonstrate, I give you a minimal example of a final Optional
implementation that does not compile for this test:
https://gist.github.com/jedws/5993596#file-gistfile1-java-L57
cheers,
jed.
On 14 July 2013 15:02, Henry Jen henry@oracle.com wrote:
I think I understand what you are saying. However, unless we make
Optional not final, the extends part just doesn't matter.
You probably know that the example provided is not completed ported to
work with our Optional implementation, and fugue works around the type
system with Option as abstract class.
Cheers,
Henry
On Jul 13, 2013, at 4:35 PM, Jed Wesley-Smith
j...@wesleysmith.ioj...@wesleysmith.iowrote:
I did supply a test that you can use to try it.
What we are talking about is whether type BoxParent is substitutable
by BoxChild in the contravariant position. Intuitively we think we only
need Box? extends Parent because we only care about the type parameter,
but the type – as you point out – is actually different. BoxParent is not
inherited by BoxChild.
Specifically, if we have a consuming Box, and we replace it with a Box
of a more specific type parameter, we could attempt feed the more general
type into it, ie. a BoxChild isn't going to appreciate having Parent fed
to it. This is why covariance and mutable containers don't mix well, and
why Java's covariant arrays are problematic.
In this situation we have an immutable container, and we can substitute
the type of our container with one of a more specific type, as it will only
ever supply a value – and a value of Child will suffice as a Parent. So,
for this case we need a Box that is substitutable, and therefore we need to
add the covariance to our box.
? extends Box is simply adding covariance to our Box type.
For a much better explanation than I can give about this, see this
excellent post describing generics in Scala, which – apart from have
declaration-site variance and using [A] in place of A – generally follow
the same pattern:
http://termsandtruthconditions.herokuapp.com/blog/2012/12/29/covariance-and-contravariance-in-scala/
cheers,
jed.
On 14 July 2013 04:49, Henry Jen henry@oracle.com wrote:
I think the type you talking about here is Optional? extends U instead
of ? extends OptionalU.
IIRC, Optional? extends U is not a subtype of OptionalU, just like
any other Collection class. ListChild is not a ListParent.
Cheers,
Henry
On Jul 13, 2013, at 3:15 AM, Jed Wesley-Smith j...@wesleysmith.io
wrote:
The ? extends Optional is unnecessary in flatMap as Optional is final.
interestingly enough, it actually is.
try the following test:
class OptionalTest {
class Parent {};
class Child extends Parent {};
@Test public void covariantReturn() {
OptionalParent some = some(new Parent());
FunctionParent, OptionalChild f = new FunctionParent,
OptionalChild() {
@Override public OptionalChild apply(Parent p) {
return some(new Child());
}
};
OptionalParent mapped = some.Parent flatMap(f);
assertThat(mapped.get(), notNullValue());
}
}
adapted from the fugue test suite:
https://bitbucket.org/atlassian/fugue/src/96a65067fb7aaf1edae1bffa07167a5865cbebec/src/test/java/com/atlassian/fugue/OptionTest.java#cl-155
The point to remember is that OptionalChild is a type and as such is
actually a subtype of OptionalParent – and therefore requires a
covariant return.
cheers,
jed.
On 13 July 2013 04:15, Mike Duigou mike.dui...@oracle.com wrote:
The ? extends Optional is unnecessary in flatMap as Optional is final.
Otherwise this looks good.
Mike
On Jul 5 2013, at 14:37 , Henry Jen wrote:
Hi,
Please review the webrev at
http://cr.openjdk.java.net/~henryjen/ccc/8015317.0/webrev/
Which adds following method to Optional,
public static T OptionalT ofNullable(T value) {}
public OptionalT filter(Predicate? super T predicate) {}
publicU OptionalU map(Function? super T, ? extends U mapper) {}
publicU OptionalU flatMap(Function? super T, ? extends
OptionalU
mapper) {}
Also included is some
Re: RFR: 8015317: Optional.filter, map, and flatMap
The ? extends Optional is unnecessary in flatMap as Optional is final.
interestingly enough, it actually is.
try the following test:
class OptionalTest {
class Parent {};
class Child extends Parent {};
@Test public void covariantReturn() {
OptionalParent some = some(new Parent());
FunctionParent, OptionalChild f = new FunctionParent,
OptionalChild() {
@Override public OptionalChild apply(Parent p) {
return some(new Child());
}
};
OptionalParent mapped = some.Parent flatMap(f);
assertThat(mapped.get(), notNullValue());
}
}
adapted from the fugue test suite:
https://bitbucket.org/atlassian/fugue/src/96a65067fb7aaf1edae1bffa07167a5865cbebec/src/test/java/com/atlassian/fugue/OptionTest.java#cl-155
The point to remember is that OptionalChild is a type and as such is
actually a subtype of OptionalParent – and therefore requires a
covariant return.
cheers,
jed.
On 13 July 2013 04:15, Mike Duigou mike.dui...@oracle.com wrote:
The ? extends Optional is unnecessary in flatMap as Optional is final.
Otherwise this looks good.
Mike
On Jul 5 2013, at 14:37 , Henry Jen wrote:
Hi,
Please review the webrev at
http://cr.openjdk.java.net/~henryjen/ccc/8015317.0/webrev/
Which adds following method to Optional,
public static T OptionalT ofNullable(T value) {}
public OptionalT filter(Predicate? super T predicate) {}
publicU OptionalU map(Function? super T, ? extends U mapper) {}
publicU OptionalU flatMap(Function? super T, ? extends OptionalU
mapper) {}
Also included is some cleanup on javadoc.
Cheers,
Henry
Re: RFR: 8015317: Optional.filter, map, and flatMap
ignore me, you do actually need both ? extends on the type constructor and
the inner type – dunno what I was thinking.
On 15 July 2013 13:02, Jed Wesley-Smith j...@wesleysmith.io wrote:
I'm not entirely sure that is a problem, have a look at the following:
https://gist.github.com/jedws/5993596#file-variancetest-java
it is only the one with a covariance annotation on the parameter that
fails…
On 15 July 2013 12:52, Zhong Yu zhong.j...@gmail.com wrote:
Another example of possible missing a wildcard
http://gee.cs.oswego.edu/dl/jsr166/dist/docs/java/util/concurrent/CompletionStage.html#thenCompose%28java.util.function.Function%29
thenCompose(Function? super T,? extends CompletionStageU fn)
should be
thenCompose(Function? super T,? extends CompletionStage? extends U
fn)
The problem is probably wide spread, and we need a tool to find these
mistakes.
Zhong Yu
On Sun, Jul 14, 2013 at 8:04 AM, Jed Wesley-Smith j...@wesleysmith.io
wrote:
(accidentally didn't post to the list)
You probably know that the example provided is not completed ported to
work with our Optional implementation,
It should be, for the example I wrote an Optional that is final and
should
be otherwise identical. It should certainly be fairly easy for any
committer to try. If you can make it work without the ? extends Optional
I'd love an explanation of how.
and fugue works around the type system with Option as abstract class.
As I've tried to explain, this isn't about the implementation of the
container class, but how covariance works with a parameterised class.
We originally had the non-, but in a discussion with Brian he alerted
us to
the fact that the signature was wrong. We hastily fixed it:
https://bitbucket.org/atlassian/fugue/commits/9eca663326a5baeb8f23974732ec585d5627a05c
To further demonstrate, I give you a minimal example of a final Optional
implementation that does not compile for this test:
https://gist.github.com/jedws/5993596#file-gistfile1-java-L57
cheers,
jed.
On 14 July 2013 15:02, Henry Jen henry@oracle.com wrote:
I think I understand what you are saying. However, unless we make
Optional not final, the extends part just doesn't matter.
You probably know that the example provided is not completed ported to
work with our Optional implementation, and fugue works around the type
system with Option as abstract class.
Cheers,
Henry
On Jul 13, 2013, at 4:35 PM, Jed Wesley-Smith j...@wesleysmith.io
j...@wesleysmith.iowrote:
I did supply a test that you can use to try it.
What we are talking about is whether type BoxParent is substitutable
by BoxChild in the contravariant position. Intuitively we think we
only
need Box? extends Parent because we only care about the type
parameter,
but the type – as you point out – is actually different. BoxParent
is not
inherited by BoxChild.
Specifically, if we have a consuming Box, and we replace it with a Box
of a more specific type parameter, we could attempt feed the more
general
type into it, ie. a BoxChild isn't going to appreciate having Parent
fed
to it. This is why covariance and mutable containers don't mix well,
and
why Java's covariant arrays are problematic.
In this situation we have an immutable container, and we can
substitute
the type of our container with one of a more specific type, as it will
only
ever supply a value – and a value of Child will suffice as a Parent.
So,
for this case we need a Box that is substitutable, and therefore we
need to
add the covariance to our box.
? extends Box is simply adding covariance to our Box type.
For a much better explanation than I can give about this, see this
excellent post describing generics in Scala, which – apart from have
declaration-site variance and using [A] in place of A – generally
follow
the same pattern:
http://termsandtruthconditions.herokuapp.com/blog/2012/12/29/covariance-and-contravariance-in-scala/
cheers,
jed.
On 14 July 2013 04:49, Henry Jen henry@oracle.com wrote:
I think the type you talking about here is Optional? extends U
instead
of ? extends OptionalU.
IIRC, Optional? extends U is not a subtype of OptionalU, just
like
any other Collection class. ListChild is not a ListParent.
Cheers,
Henry
On Jul 13, 2013, at 3:15 AM, Jed Wesley-Smith j...@wesleysmith.io
wrote:
The ? extends Optional is unnecessary in flatMap as Optional is
final.
interestingly enough, it actually is.
try the following test:
class OptionalTest {
class Parent {};
class Child extends Parent {};
@Test public void covariantReturn() {
OptionalParent some = some(new Parent());
FunctionParent, OptionalChild f = new FunctionParent,
OptionalChild() {
@Override public OptionalChild apply(Parent p) {
return some(new Child
Re: RFR : JDK-8001642 : Add OptionalT, OptionalDouble, OptionalInt, OptionalLong
There is no need for an Option container to show how nested collections may be
misused, you could just as easily show an example of a ListListListT that
is isomorphic to a flattened IterableT . I'd simply point to the utility of
the monadic bind or flatMap function!
There are several reasons why Option types provide serious usability
improvements over null, notwithstanding annotation support. The first is that
the type-system prevents misuse (modulo unsafe API), and the second is that it
allows operations that produce optional results to be sequenced easily without
if checks. For mor information see previous posts on Optional forming a Monad.
cheers,
jed.
On 06/03/2013, at 10:58 PM, Remi Forax fo...@univ-mlv.fr wrote:
On 03/06/2013 11:54 AM, Jed Wesley-Smith wrote:
Really, this is a lot of fuss over nothing.
There is actually no fundamental difference between Scala's Option, Guava's
Optional, Fugue's Option, Java's Optional and Haskell's Maybe – they are
modelling the same thing, the possibility of a value not being present.
The fact that there may be minor differences in api or semantics around
whether null is a legal value are minor in the scheme of things (and yes,
null is a pretty stupid legal value of a Some IMHO).
Stephen's example is ludicrous, why have a list of optional values? You'd
flatten down into just a list – and an optional list only makes sense if the
enclosed list is guaranteed to be non-empty, otherwise you just return an
empty list!
People like shooting their own feet.
http://cs.calstatela.edu/wiki/index.php/Courses/CS_460/Fall_2012/Week_8/gamePlay.combat.BattleAnalysis
If we are going to use potential straw-men as arguments we can stall all
progress. Please concentrate on the important matters, let's disavow null as
a valid value and save us all a billion dollars
Also Scala Option is not the only way to solve the null problem.
The JSR308 annotation @Nullable/@NonNull are recognized by Eclipse and
IntelliJ at least.
.
cheers,
jed.
cheers,
Rémi
On 06/03/2013, at 8:47 PM, Remi Forax fo...@univ-mlv.fr wrote:
Ok, let be nuclear on this,
There is no good reason to introduce OptionalT in java.util.
It doen't work like Google's Guava Optional despite having the same
name, it doesn't work like Scala's Option despite having a similar name,
moreover the lambda pipeline face a similar issue with the design of
collectors (see stream.collect()) but solve that similar problem with a
different design, so the design of Optional is not even consistent with
the rest of the stream API.
So why do we want something like Optional, we want it to be able to
represent the fact that as Mike states a returning result can have no
value by example Colections.emptyList().stream().findFirst() should
'return' no value.
As Stephen Colebourne said, Optional is a bad name because Scala uses
Option [1] which can used in the same context, as result of a filter/map
etc. but Option in Scala is a way to mask null. Given the name
proximity, people will start to use Optional like Option in Scala and we
will see methods returning things like OptionalListOptionalString.
Google's Guava, which is a popular library, defines a class named
Optional, but allow to store null unlike the current proposed
implementation, this will generate a lot of confusions and frustrations.
In fact, we don't need Optional at all, because we don't need to return
a value that can represent a value or no value,
the idea is that methods like findFirst should take a lambda as
parameter letting the user to decide what value should be returned by
findFirst if there is a value and if there is no value.
So instead of
stream.findFirst().orElse(null)
you will write
stream.findFirst(orNull)
with orNull() defined as like that
public static T Optionalizer orNull() {
return (isPresent, element) - isPresent? element: null;
}
The whole design is explained here [2] and is similar to the way
Collectors are defined [3],
it's basically the lambda way of thinking, instead of creating an object
representing the different states resulting of a call to findFirst,
findFirst takes a lambda as parameter which is fed with the states of a
call.
cheers,
Rémi
[1] http://www.scala-lang.org/api/current/index.html#scala.Option
[2]
http://mail.openjdk.java.net/pipermail/lambda-libs-spec-observers/2013-February/001470.html
[3]
http://hg.openjdk.java.net/lambda/lambda/jdk/file/tip/src/share/classes/java/util/stream/Collectors.java
On 03/04/2013 09:29 PM, Mike Duigou wrote:
Hello All;
This patch introduces Optional container objects to be used by the lambda
streams libraries for returning results.
The reference Optional type, as defined, intentionally does not allow null
values. null may be used with the Optional.orElse() method.
All of the Optional types define hashCode() and equals implementations.
Use of Optional types
Re: RFR : JDK-8001642 : Add OptionalT, OptionalDouble, OptionalInt, OptionalLong
Really, this is a lot of fuss over nothing.
There is actually no fundamental difference between Scala's Option, Guava's
Optional, Fugue's Option, Java's Optional and Haskell's Maybe – they are
modelling the same thing, the possibility of a value not being present.
The fact that there may be minor differences in api or semantics around whether
null is a legal value are minor in the scheme of things (and yes, null is a
pretty stupid legal value of a Some IMHO).
Stephen's example is ludicrous, why have a list of optional values? You'd
flatten down into just a list – and an optional list only makes sense if the
enclosed list is guaranteed to be non-empty, otherwise you just return an empty
list!
If we are going to use potential straw-men as arguments we can stall all
progress. Please concentrate on the important matters, let's disavow null as a
valid value and save us all a billion dollars.
cheers,
jed.
On 06/03/2013, at 8:47 PM, Remi Forax fo...@univ-mlv.fr wrote:
Ok, let be nuclear on this,
There is no good reason to introduce OptionalT in java.util.
It doen't work like Google's Guava Optional despite having the same
name, it doesn't work like Scala's Option despite having a similar name,
moreover the lambda pipeline face a similar issue with the design of
collectors (see stream.collect()) but solve that similar problem with a
different design, so the design of Optional is not even consistent with
the rest of the stream API.
So why do we want something like Optional, we want it to be able to
represent the fact that as Mike states a returning result can have no
value by example Colections.emptyList().stream().findFirst() should
'return' no value.
As Stephen Colebourne said, Optional is a bad name because Scala uses
Option [1] which can used in the same context, as result of a filter/map
etc. but Option in Scala is a way to mask null. Given the name
proximity, people will start to use Optional like Option in Scala and we
will see methods returning things like OptionalListOptionalString.
Google's Guava, which is a popular library, defines a class named
Optional, but allow to store null unlike the current proposed
implementation, this will generate a lot of confusions and frustrations.
In fact, we don't need Optional at all, because we don't need to return
a value that can represent a value or no value,
the idea is that methods like findFirst should take a lambda as
parameter letting the user to decide what value should be returned by
findFirst if there is a value and if there is no value.
So instead of
stream.findFirst().orElse(null)
you will write
stream.findFirst(orNull)
with orNull() defined as like that
public static T Optionalizer orNull() {
return (isPresent, element) - isPresent? element: null;
}
The whole design is explained here [2] and is similar to the way
Collectors are defined [3],
it's basically the lambda way of thinking, instead of creating an object
representing the different states resulting of a call to findFirst,
findFirst takes a lambda as parameter which is fed with the states of a
call.
cheers,
Rémi
[1] http://www.scala-lang.org/api/current/index.html#scala.Option
[2]
http://mail.openjdk.java.net/pipermail/lambda-libs-spec-observers/2013-February/001470.html
[3]
http://hg.openjdk.java.net/lambda/lambda/jdk/file/tip/src/share/classes/java/util/stream/Collectors.java
On 03/04/2013 09:29 PM, Mike Duigou wrote:
Hello All;
This patch introduces Optional container objects to be used by the lambda
streams libraries for returning results.
The reference Optional type, as defined, intentionally does not allow null
values. null may be used with the Optional.orElse() method.
All of the Optional types define hashCode() and equals implementations. Use
of Optional types in collections should be generally discouraged but having
useful equals() and hashCode() is ever so convenient.
http://cr.openjdk.java.net/~mduigou/JDK-8001642/0/webrev/
Mike
