Re: Generics question
Thanks Phillip and Bill!
That worked! :-)
And thanks for the tutorial PDF.
On May 28, 2009, at 7:17 PM, Bill Gallop wrote:
Ricardo,
Try defining your loginPageClass() like this:
public Class? extends MPVLoginPage loginPageClass() {
...
}
and override accordingly. Then Java will allow you to return any
subclass of MPVLoginPage.
Bill
From: Ricardo J. Parada [mailto:rpar...@mac.com]
To: WebObjects-Dev Apple [mailto:webobjects-...@lists.apple.com]
Sent: Thu, 28 May 2009 17:00:06 -0600
Subject: Generics question
I'm changing my code to use pageWithName(Foo.class) instead of
pageWithName(Foo) through out the code.
Then I used to have a method that return the name of the login page
which I changed to return the class of the login page. But then if
an application wants to override that I end up with stuff like this:
public ClassMPVLoginPage loginPageClass() {
return PPPLoginPage.class;
}
Here PPPLoginPage is a subclass of MPVLoginPage and I thought this
would be allowed by java but I'm getting an error and I have not
mastered generics that well yet. ;-)
Is there a better way to do this?
:-)
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Re: Curly Generics Question - Update
On 16/05/2009, at 12:07 PM, Mike Schrag wrote:
I'm not sure this is really any better ... Fundamentally there's a ?
in that param, and as a result, it's impossible to do a put in a
typesafe way. You don't know what V is. I _think_ the signature as
it is now is actually correct, but if you need to insert into that
map inside createRequest, you simply have to copy it. I don't think
it's possible to ensure compiler-enforceable type-safety in any
other way (which is to say, accurate type safety).
Mike is right, you cannot safely insert anything into a wildcard
parameterised producer type (? extends T) because you do not know
what subtype of T it is actually meant to contain. You only know that
it will produce elements that are assignable to T. If you want to
put anything, or rather have it consume values, it needs to be
parameterised with the form ? super T, which will accept values that
are assignable to T. Hence the PECS mantra, Producer extend Consumer
super. There is no way to express both a producer and consumer using
a single wildcard expression.
Consumer:
MapString, ? super ListString allows for:
m.put(foo, new ArrayListString(bar));
m.put(foo, new NSArrayString(bar));
You can safely insert anything that is a ListString
and
m = new NSDictionaryString, ListString();
but not
m = new NSDictionaryString, NSArrayString();
You cannot safely upcast from a more specific type to ListString
Producer:
MapString, ? extends ListString allows for:
ListString t = m.get(foo);
but not
NSArrayString t = m.get(foo);
Everything you retrieve will be assignable to ListString
and
m = new NSDictionaryString, NSArrayString();
m = new HashMapString, ArrayListString();
m = new NSDictionaryString, ListString();
You can safely upcast to the more generic type of MapString,
ListString
Getting back to the original example:
public WORequest createRequest(String method,String url,String
anHTTPVersion,MapString,? extends ListString someHeaders,NSData
content,MapString,Object someInfo)
It's unfortunately that the method signature of someHeaders was
changed from NSDictionary to Map because the original contract of
NSDictionary implies immutability, while Map has no such implication.
But the intent can still be derived from the type parameters as being
a producer. If you are overriding this method you should not assume
that the someHeaders Map your were passed is mutable, you should clone
it to a concrete mutable type if you wish to modify it.
On May 15, 2009, at 9:51 PM, Henrique Prange wrote:
Hi Mike,
The following solution doesn't solve the unchecked type cast
problem. But it respect PECS definition and accept a MapString,
NSArrayString as parameter. Do you think it is reasonable?
public V extends ListString WORequest treateRequest(String
method, String url, String anHTTPVersion, MapString, ? super V
someHeaders, NSData content, MapString, Object someInfo) {
...
someHeaders.put(foo, (V) Collections.singletonList(bar));
...
}
Cheers,
Henrique
On May 15, 2009, at 8:29 PM, Mike Schrag wrote:
Map String, List String correctHeaders = new HashMap
String, List String ();
btw, this is what i was saying that the only typesafe way to do
this is to copy the original headers -- so you would do new
HashMapString, ListString(originalHeaders) and then you'd have
a properly typesafe String, ListString that you can happily
insert into whatever ListString subtypes you want inside of
createRequest. But it takes a copy to do it, which kind of sucks.
ms
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Re: Curly Generics Question - Update
you should clone it to a concrete mutable type if you wish to modify it. have fun with this btw ... the cherry on top is that you can't even reliably CLONE these stupid things, because 1) cloning in java is retarded and 2) even if you can clone, you might just be cloning an immutable map (if they passed in NSDict, cloning doesn't get you far). I think you literally have to just copy it into a new NSMutableDict or a HashMap, which, of course, throws away Anjo's dream of passing in a TreeMap. ms ___ Do not post admin requests to the list. They will be ignored. Webobjects-dev mailing list (Webobjects-dev@lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/webobjects-dev/archive%40mail-archive.com This email sent to arch...@mail-archive.com
Re: Curly Generics Question - Update
Hi Andrew,
I find it odd that the map should have ? extends ListString as a
parameter as the extension ought to be unnecessary (assuming callers
are working to the List interface) - any List implementation with a
String parameter fulfills ListString. I like generics too, but have
come across similarly gnarly counter-intuitive things. I find that
often if you think about them enough they eventually make sense, but
this one has me stumped!
I see it came from overriding the WOApplication method - and if you
don't include the parameter in this way you get a compilation error.
This can be made to go away by overriding without providing the
generic parameters, which then produces a warning which you can
annotate away:
@SuppressWarnings(unchecked)
@Override
public WORequest createRequest(String method, String aurl,
String anHTTPVersion,
Map someHeaders, NSData content,
Map someInfo) {
someHeaders.put(foo,
Collections.StringsingletonList(bar));
I suppose you might want to use this kind of wildcard extension if you
want to pass a Map which declares an extension of List elsewhere; e.g.
if there was a calling method which was passing a variable declared as
MapString, NSMutableArrayString to this method there would be a
compilation error without the wildcard; arguably what the calling
method ought to be doing though is declaring the list it passes as
MapString, ListString and hiding the concrete List implementation,
negating the need for the wildcard.
e.g. works to impl rather than interface:
NSMutableDictionaryString, NSMutableArrayString someHeaders =
new NSMutableDictionaryString, NSMutableArrayString();
someHeaders.setObjectForKey(new NSMutableArrayString(bar),
foo);
WORequest req = createRequest(method, aurl, anHTTPVersion,
someHeaders, content, someInfo);
vs. working just to interface:
MapString, ListString someHeaders = new
NSMutableDictionaryString, ListString();
someHeaders.put(foo, new NSMutableArrayString(bar));
WORequest req = createRequest(method, aurl, anHTTPVersion,
someHeaders, content, someInfo);
Both compile to current WOApplication API; former would not if the
wildcard were to be removed from createRequest.
Could this be considered a bug in WOApplication? I believe if this
method declaration had the wildcard extension removed and any calling
methods which need to be were fixed to work to interface rather than
implementation then this problem would go away and createRequest could
be overridden and worked with generically. Easy to say - I still find
myself preferring to work directly with NS implementations for key-
value-coding / EOQualifiers...
Cheers,
Jim
On 15 May 2009, at 03:54, Andrew Lindesay wrote:
Sorry wrong method; I obviously meant put rather than add in
this example and The method put(String,ListString) in the type
MapString,capture#1-of? extends ListString is not applicable for
the arguments (String,ListString) is the problem.
I've been working with generics for quite a while (and quite like
them) but this one has me stumped!
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Re: Curly Generics Question - Update
Hello Jim; Thanks for the reply. what the calling method ought to be doing though is declaring the list it passes as MapString, ListString and hiding the concrete List implementation, negating the need for the wildcard. I tried it with a concrete implementation of List as well, but this also raised an error in a similar fashion. It's got me. You are right, I could create a new Map and use that instead as it should work, but that would be rather inelegant. Could this be considered a bug in WOApplication? Yes, I think it is not quite right. cheers. ___ Andrew Lindesay www.lindesay.co.nz ___ Do not post admin requests to the list. They will be ignored. Webobjects-dev mailing list (Webobjects-dev@lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/webobjects-dev/archive%40mail-archive.com This email sent to arch...@mail-archive.com
Re: Curly Generics Question - Update
Yeah this is a tricky one ... But you're right that the API is ?
extends ListString so you can pass in NSArrayString, which is a
pretty common implementation. You also can't necessarily just assume
people can declare their vars as ListString instead of
NSArrayString because you don't know where that var came from (the
general case is that you really do want it to be enforced as String,
NSArrayString). Basically, this method declaration makes it easy
and flexible for people passing in params, but it makes it really
complicated to add values to that map like Andrew is finding. The
deal is that the signature is ? extends ListString this does NOT
mean you can just put anything that extends ListString into the
value, rather, it means you can pass in any generic that has a List
that is a subclass of ListString. The distinction is that if you
pass in NSArrayString as the list, you can't just put any list into
it -- it explicitly has to be an NSArrayString, but inside that
method, you have no idea what the ACTUAL type is. So Andrew's code is
failing because the list type he's putting in is whatever
singletonList returns, but that's not guaranteed to be match the
passed-in type.
The problem is that if the method sig is changed to String,
ListString then you have to do a copy operation to convert String,
NSArrayString to String, ListString ... Tough call on that
one. If the method sig changes, it's annoying to people passing
values in, but as it stands, i'm not sure it's possible to put values
INTO it inside this method.
ms
On May 15, 2009, at 8:14 AM, Jim Kinsey wrote:
Hi Andrew,
I find it odd that the map should have ? extends ListString as a
parameter as the extension ought to be unnecessary (assuming callers
are working to the List interface) - any List implementation with a
String parameter fulfills ListString. I like generics too, but
have come across similarly gnarly counter-intuitive things. I find
that often if you think about them enough they eventually make
sense, but this one has me stumped!
I see it came from overriding the WOApplication method - and if you
don't include the parameter in this way you get a compilation error.
This can be made to go away by overriding without providing the
generic parameters, which then produces a warning which you can
annotate away:
@SuppressWarnings(unchecked)
@Override
public WORequest createRequest(String method, String aurl,
String anHTTPVersion,
Map someHeaders, NSData content,
Map someInfo) {
someHeaders.put(foo,
Collections.StringsingletonList(bar));
I suppose you might want to use this kind of wildcard extension if
you want to pass a Map which declares an extension of List
elsewhere; e.g. if there was a calling method which was passing a
variable declared as MapString, NSMutableArrayString to this
method there would be a compilation error without the wildcard;
arguably what the calling method ought to be doing though is
declaring the list it passes as MapString, ListString and hiding
the concrete List implementation, negating the need for the wildcard.
e.g. works to impl rather than interface:
NSMutableDictionaryString, NSMutableArrayString someHeaders =
new NSMutableDictionaryString, NSMutableArrayString();
someHeaders.setObjectForKey(new NSMutableArrayString(bar),
foo);
WORequest req = createRequest(method, aurl, anHTTPVersion,
someHeaders, content, someInfo);
vs. working just to interface:
MapString, ListString someHeaders = new
NSMutableDictionaryString, ListString();
someHeaders.put(foo, new NSMutableArrayString(bar));
WORequest req = createRequest(method, aurl, anHTTPVersion,
someHeaders, content, someInfo);
Both compile to current WOApplication API; former would not if the
wildcard were to be removed from createRequest.
Could this be considered a bug in WOApplication? I believe if this
method declaration had the wildcard extension removed and any
calling methods which need to be were fixed to work to interface
rather than implementation then this problem would go away and
createRequest could be overridden and worked with generically. Easy
to say - I still find myself preferring to work directly with NS
implementations for key-value-coding / EOQualifiers...
Cheers,
Jim
On 15 May 2009, at 03:54, Andrew Lindesay wrote:
Sorry wrong method; I obviously meant put rather than add in
this example and The method put(String,ListString) in the type
MapString,capture#1-of? extends ListString is not applicable
for the arguments (String,ListString) is the problem.
I've been working with generics for quite a while (and quite like
them) but this one has me stumped!
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Re: Curly Generics Question - Update
Hi Andrew,
what the calling method ought to be doing though is declaring the
list it passes as MapString, ListString and hiding the concrete
List implementation, negating the need for the wildcard.
I tried it with a concrete implementation of List as well, but this
also raised an error in a similar fashion. It's got me. You are
right, I could create a new Map and use that instead as it should
work, but that would be rather inelegant.
I was meaning that as more of an example of why, possibly, the
bug (I'm not sure it really can be called that yet) exists - that
there was some calling code somewhere in the WO source which was
passing in something declared a bit too concrete, so it got fixed by
wildcarding the List parameter on createRequest rather than changing
the declaration in the calling code to work to an interface.
I think the only real solution which still involves overriding
createRequest is to override without generics and suppress the
warning; if you want to do lots of work within the overridden
createRequest and like to have the generic type checking then you
could pass this work on to a different method with appropriately
generic arguments:
@SuppressWarnings(unchecked)
@Override
public WORequest createRequest(String method, String aurl,
String anHTTPVersion,
Map someHeaders, NSData content,
Map someInfo) {
return genericCreateRequest(method, aurl, anHTTPVersion,
someHeaders, content, someInfo);
}
private WORequest genericCreateRequest(String method, String aurl,
String anHTTPVersion,
MapString, ListString someHeaders, NSData content,
MapString, Object someInfo) {
someHeaders.put(foo,
Collections.StringsingletonList(bar));
return super.createRequest(method, aurl, anHTTPVersion, someHeaders,
content, someInfo);
}
Cheers,
Jim
Could this be considered a bug in WOApplication?
Yes, I think it is not quite right.
cheers.
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Re: Curly Generics Question - Update
well, no matter what you do, i think you're going to throw out type
safety, so inside the method, you could just cast the headers to
String, ListString :
MapString, ListString badCast = (MapString,
ListString)headers;
badCast.put(a, new LinkedListString());
ms
On May 15, 2009, at 8:56 AM, Jim Kinsey wrote:
Hi Andrew,
what the calling method ought to be doing though is declaring the
list it passes as MapString, ListString and hiding the
concrete List implementation, negating the need for the wildcard.
I tried it with a concrete implementation of List as well, but this
also raised an error in a similar fashion. It's got me. You are
right, I could create a new Map and use that instead as it should
work, but that would be rather inelegant.
I was meaning that as more of an example of why, possibly, the
bug (I'm not sure it really can be called that yet) exists - that
there was some calling code somewhere in the WO source which was
passing in something declared a bit too concrete, so it got fixed
by wildcarding the List parameter on createRequest rather than
changing the declaration in the calling code to work to an interface.
I think the only real solution which still involves overriding
createRequest is to override without generics and suppress the
warning; if you want to do lots of work within the overridden
createRequest and like to have the generic type checking then you
could pass this work on to a different method with appropriately
generic arguments:
@SuppressWarnings(unchecked)
@Override
public WORequest createRequest(String method, String aurl,
String anHTTPVersion,
Map someHeaders, NSData content,
Map someInfo) {
return genericCreateRequest(method, aurl, anHTTPVersion,
someHeaders, content, someInfo);
}
private WORequest genericCreateRequest(String method, String aurl,
String anHTTPVersion,
MapString, ListString someHeaders, NSData content,
MapString, Object someInfo) {
someHeaders.put(foo,
Collections.StringsingletonList(bar));
return super.createRequest(method, aurl, anHTTPVersion,
someHeaders, content, someInfo);
}
Cheers,
Jim
Could this be considered a bug in WOApplication?
Yes, I think it is not quite right.
cheers.
___
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www.lindesay.co.nz
http://www.bbc.co.uk
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Re: Curly Generics Question - Update
On 15/05/2009, at 10:48 PM, Mike Schrag wrote:
Yeah this is a tricky one ... But you're right that the API is ?
extends ListString so you can pass in NSArrayString, which is a
pretty common implementation. You also can't necessarily just
assume people can declare their vars as ListString instead of
NSArrayString because you don't know where that var came from (the
general case is that you really do want it to be enforced as
String, NSArrayString). Basically, this method declaration
makes it easy and flexible for people passing in params, but it
makes it really complicated to add values to that map like Andrew is
finding. The deal is that the signature is ? extends ListString
this does NOT mean you can just put anything that extends
ListString into the value, rather, it means you can pass in any
generic that has a List that is a subclass of ListString. The
distinction is that if you pass in NSArrayString as the list, you
can't just put any list into it -- it explicitly has to be an
NSArrayString, but inside that method, you have no idea what the
ACTUAL type is. So Andrew's code is failing because the list type
he's putting in is whatever singletonList returns, but that's not
guaranteed to be match the passed-in type.
The problem is that if the method sig is changed to String,
ListString then you have to do a copy operation to convert
String, NSArrayString to String, ListString ... Tough call
on that one.
No, no - you wouldn't have to do that at all. This is a bug.
// test interface
private static interface NSListT extends ListT
{
public int count();
}
@Override
public WORequest createRequest( String method,
String aurl,
String anHttpVersion,
Map String, ? extends List String
someHeaders,
NSData content,
Map String, Object someInfo )
{
Map String, List String correctHeaders = new HashMap String,
List String ();
NSListString nslist = null;
someHeaders.put( foo, nslist ); // compile error
correctHeaders.put( foo, nslist ); // no problems
NSMutableArrayString array = null;
someHeaders.put( foo, array ); // compile error
correctHeaders.put( foo, array ); // no problems
}
You don't need extends for interfaces AFAIK.
If the method sig changes, it's annoying to people passing values in,
Map String, NSArray String someHeaders = null;
Map String, Object someInfo = null;
createRequest( foo, url, 1, someHeaders, null, someInfo );
No compile errors.
I'm not convinced that fixing the method signature would break
anything for anyone at all.
but as it stands, i'm not sure it's possible to put values INTO it
inside this method.
ms
with regards,
--
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Re: Curly Generics Question - Update
public WORequest createRequest( String method,
String aurl,
String anHttpVersion,
Map String, ? extends List String
someHeaders,
NSData content,
Map String, Object someInfo )
{
Map String, List String correctHeaders = new HashMap String,
List String ();
NSListString nslist = null;
someHeaders.put( foo, nslist ); // compile error
correctHeaders.put( foo, nslist ); // no problems
NSMutableArrayString array = null;
someHeaders.put( foo, array ); // compile error
correctHeaders.put( foo, array ); // no problems
}
You don't need extends for interfaces AFAIK.
Not sure what you're showing here, but you are correct that you don't
need extends to control the value you put into the map. You need the
extends to control what generic impls you can pass in as the PARAMETER
to the method. So if you're showing that a MapString, ListString
allows you to put a subtype of List as the value, I totally agree.
The problem is that a MapString, NSArrayString is NOT assignable
to a MapString, ListString -- this is the Integer vs Number
problem*, and it's not a typesafe operation. In your example, map a
MapString, NSArrayString and try to pass that into createRequest
-- it will work, but you can't insert into it, because you have no
idea precisely what subtype of List the generic was actually written
for -- the ? extends screws your ability to insert into it in a
typesafe way. If you remove the ? extends you can put any list
subtype into the value, but you can't pass in a generic that is
declared as anything except PRECISELY String, ListString, which
causes the problem below:
If the method sig changes, it's annoying to people passing values in,
Map String, NSArray String someHeaders = null;
Map String, Object someInfo = null;
createRequest( foo, url, 1, someHeaders, null, someInfo );
No compile errors.
I'm not convinced that fixing the method signature would break
anything for anyone at all.
public static void doSomething() {
MapString, LinkedListString testMap = new HashMapString,
LinkedListString();
doSomethingElse(testMap);
}
public static void doSomethingElse(MapString, ListString test) {
}
this is a compile error .. if the method signature removes the ?
extends List you can't pass in a generic that has a V that is
explicitly declared as a subtype of List, you can only pass in a V
that is declared as List.
ms
* I keep this in my Stickies in like 24pt type, so every time I say
WTF CAN'T I DO THAT, i can run stickies and remind myself:
WHY IT'S ILLEGAL TO UPCAST GENERICS
MapString, Integer integers = new HashMapString, Integer();
MapString, Number numbers = integers; // illegal
numbers.put(str, Long.valueOf(1)); // and this is why
now a long is in integers ___
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Re: Curly Generics Question - Update
Map String, List String correctHeaders = new HashMap String, List String (); btw, this is what i was saying that the only typesafe way to do this is to copy the original headers -- so you would do new HashMapString, ListString(originalHeaders) and then you'd have a properly typesafe String, ListString that you can happily insert into whatever ListString subtypes you want inside of createRequest. But it takes a copy to do it, which kind of sucks. ms ___ Do not post admin requests to the list. They will be ignored. Webobjects-dev mailing list (Webobjects-dev@lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/webobjects-dev/archive%40mail-archive.com This email sent to arch...@mail-archive.com
Re: Curly Generics Question - Update
On 16/05/2009, at 9:27 AM, Mike Schrag wrote:
public WORequest createRequest( String method,
String aurl,
String anHttpVersion,
Map String, ? extends List String
someHeaders,
NSData content,
Map String, Object someInfo )
{
Map String, List String correctHeaders = new HashMap String,
List String ();
NSListString nslist = null;
someHeaders.put( foo, nslist ); // compile error
correctHeaders.put( foo, nslist ); // no problems
NSMutableArrayString array = null;
someHeaders.put( foo, array ); // compile error
correctHeaders.put( foo, array ); // no problems
}
You don't need extends for interfaces AFAIK.
Not sure what you're showing here, but you are correct that you
don't need extends to control the value you put into the map. You
need the extends to control what generic impls you can pass in as
the PARAMETER to the method.
Ugh - yeah. Helps if I save the editor :-)
So if you're showing that a MapString, ListString allows you to
put a subtype of List as the value, I totally agree. The problem is
that a MapString, NSArrayString is NOT assignable to a
MapString, ListString -- this is the Integer vs Number problem*,
and it's not a typesafe operation.
Right - lights are back on now. Cool.
* I keep this in my Stickies in like 24pt type, so every time I say
WTF CAN'T I DO THAT, i can run stickies and remind myself:
WHY IT'S ILLEGAL TO UPCAST GENERICS
MapString, Integer integers = new HashMapString, Integer();
MapString, Number numbers = integers; // illegal
numbers.put(str, Long.valueOf(1)); // and this is why
now a long is in integers
Generics are great mostly - but there are times when it's just
downright annoying :-).
with regards,
--
Lachlan Deck
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Re: Curly Generics Question - Update
On May 15, 2009, at 4:59 PM, Lachlan Deck wrote: Generics are great mostly - but there are times when it's just downright annoying :-). Sounds like Maven! :-P -- Chuck Hill Senior Consultant / VP Development Come to WOWODC'09 in San Fran this June! http://www.wocommunity.org/wowodc09/ ___ Do not post admin requests to the list. They will be ignored. Webobjects-dev mailing list (Webobjects-dev@lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/webobjects-dev/archive%40mail-archive.com This email sent to arch...@mail-archive.com
Re: Curly Generics Question - Update
On 16/05/2009, at 10:03 AM, Chuck Hill wrote: On May 15, 2009, at 4:59 PM, Lachlan Deck wrote: Generics are great mostly - but there are times when it's just downright annoying :-). Sounds like Maven! :-P Touché ;-) But still lovin' your work as the unlikely ambassador, finding every opportunity .. Maven here, maven there, maven loving everywhere ;-) with regards, -- Lachlan Deck ___ Do not post admin requests to the list. They will be ignored. Webobjects-dev mailing list (Webobjects-dev@lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/webobjects-dev/archive%40mail-archive.com This email sent to arch...@mail-archive.com
Re: Curly Generics Question - Update
Hi Mike,
The following solution doesn't solve the unchecked type cast problem.
But it respect PECS definition and accept a MapString,
NSArrayString as parameter. Do you think it is reasonable?
public V extends ListString WORequest treateRequest(String
method, String url, String anHTTPVersion, MapString, ? super V
someHeaders, NSData content, MapString, Object someInfo) {
...
someHeaders.put(foo, (V) Collections.singletonList(bar));
...
}
Cheers,
Henrique
On May 15, 2009, at 8:29 PM, Mike Schrag wrote:
Map String, List String correctHeaders = new HashMap String,
List String ();
btw, this is what i was saying that the only typesafe way to do this
is to copy the original headers -- so you would do new
HashMapString, ListString(originalHeaders) and then you'd have a
properly typesafe String, ListString that you can happily insert
into whatever ListString subtypes you want inside of
createRequest. But it takes a copy to do it, which kind of sucks.
ms
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Re: Curly Generics Question - Update
I'm not sure this is really any better ... Fundamentally there's a ?
in that param, and as a result, it's impossible to do a put in a
typesafe way. You don't know what V is. I _think_ the signature as it
is now is actually correct, but if you need to insert into that map
inside createRequest, you simply have to copy it. I don't think it's
possible to ensure compiler-enforceable type-safety in any other way
(which is to say, accurate type safety).
ms
On May 15, 2009, at 9:51 PM, Henrique Prange wrote:
Hi Mike,
The following solution doesn't solve the unchecked type cast
problem. But it respect PECS definition and accept a MapString,
NSArrayString as parameter. Do you think it is reasonable?
public V extends ListString WORequest treateRequest(String
method, String url, String anHTTPVersion, MapString, ? super V
someHeaders, NSData content, MapString, Object someInfo) {
...
someHeaders.put(foo, (V) Collections.singletonList(bar));
...
}
Cheers,
Henrique
On May 15, 2009, at 8:29 PM, Mike Schrag wrote:
Map String, List String correctHeaders = new HashMap
String, List String ();
btw, this is what i was saying that the only typesafe way to do
this is to copy the original headers -- so you would do new
HashMapString, ListString(originalHeaders) and then you'd have
a properly typesafe String, ListString that you can happily
insert into whatever ListString subtypes you want inside of
createRequest. But it takes a copy to do it, which kind of sucks.
ms
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Re: Curly Generics Question - Update
Am 16.05.2009 um 01:29 schrieb Mike Schrag: Map String, List String correctHeaders = new HashMap String, List String (); btw, this is what i was saying that the only typesafe way to do this is to copy the original headers -- so you would do new HashMapString, ListString(originalHeaders) and then you'd have a properly typesafe String, ListString that you can happily insert into whatever ListString subtypes you want inside of createRequest. But it takes a copy to do it, which kind of sucks. As the whole point of this stupid and annoying API change to Map was that you could maintain order of the parameters, I'd at least use a TreeMap :) Cheers, Anjo ___ Do not post admin requests to the list. They will be ignored. Webobjects-dev mailing list (Webobjects-dev@lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/webobjects-dev/archive%40mail-archive.com This email sent to arch...@mail-archive.com
Curly Generics Question
I've been working with generics for quite a while (and quite like
them) but this one has me stumped!
public WORequest createRequest(String method,String url,String
anHTTPVersion,MapString,? extends ListString someHeaders,NSData
content,MapString,Object someInfo)
{
...
someHeaders.add(foo, Collections.StringsingletonList(bar));
...
}
This causes a compile error The method add(String,ListString) is
undefined for the type MapString,capture#1-of? extends
ListString. Any help appreciated!
cheers.
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www.lindesay.co.nz
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Re: Curly Generics Question - Update
Sorry wrong method; I obviously meant put rather than add in this example and The method put(String,ListString) in the type MapString,capture#1-of? extends ListString is not applicable for the arguments (String,ListString) is the problem. I've been working with generics for quite a while (and quite like them) but this one has me stumped! ___ Andrew Lindesay www.lindesay.co.nz ___ Do not post admin requests to the list. They will be ignored. Webobjects-dev mailing list (Webobjects-dev@lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/webobjects-dev/archive%40mail-archive.com This email sent to arch...@mail-archive.com
Generics Question
Hi, Will someone please help me here? How do I do the following without getting the pesky warning from Eclipse about unchecked type conversion? NSArrayNewsKeywords newsKeywords = EOUtilities .objectsForEntityNamed (EOSharedEditingContext.defaultSharedEditingContext(), NewsKeywords); Thanks in advance, Jon ___ Do not post admin requests to the list. They will be ignored. Webobjects-dev mailing list (Webobjects-dev@lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/webobjects-dev/archive%40mail-archive.com This email sent to [EMAIL PROTECTED]
Re: Generics Question
On Dec 20, 2007, at 2:03 PM, Jonathan Miller wrote: How do I do the following without getting the pesky warning from Eclipse about unchecked type conversion? NSArrayNewsKeywords newsKeywords = EOUtilities .objectsForEntityNamed (EOSharedEditingContext.defaultSharedEditingContext(), NewsKeywords); I wouldn't do the above in the first place. Just because an EOSharedEditingContext extends EOEditingContext doesn't mean that it IS an EOEditingContext. It's actually quite different and can be the cause of considerable grief when not handled correctly (deadlocks and other nasty behaviors). It's probably best to fetch shared objects only early in an app's life (e.g., in the Application constructor) or to mark objects as shared in one's eomodel which will cause them all to be fetched when the first shared object is fetched. NewsKeywords should be fetched into an EOSharedEditingContext using its thread-safe API, objectsWithFetchSpecification() or bindObjectsWithFetchSpecification(), and these fetched objects accessed only using the thread-safe API, objectsByEntityName() or objectsByEntityNameAndFetchSpecificationName(). You may be able to avoid the unchecked type conversion warnings by doing so as well. Aloha, Art ___ Do not post admin requests to the list. They will be ignored. Webobjects-dev mailing list (Webobjects-dev@lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/webobjects-dev/archive%40mail-archive.com This email sent to [EMAIL PROTECTED]
