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• Plist array , cannot change dictonaries inside

  - by Andy Jacobs

  i have a plist that's at its root an array with dictonaries inside it. i load a plist from my recourses as an NSMutableArray. [NSMutableArray arrayWithContentsOfFile:[[NSBundle mainBundle] pathForResource:@"Filters" ofType:@"plist"]] i store it into nsuserdefault because it has to be persistent between startups. [[NSUserDefaults standardUserDefaults] setObject:array forKey:@"filters"]; but i can't change the dictonaries in the array because they are not mutable. how can i make them mutable?

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• Looking for detailed explanation of Hibernate UserType methods for mutable objects

  - by Tom

  I am creating a custom UserType class in Hibernate. The specific case is for an HL7v3 clinical document (I work in health IT). It is a mutable object and most of the documentation around the Hibernate UserType interface seems to center around immutable types. I want a better understanding of how and when the interface methods are used, specifically: assemble - why two parameters (one Serializable, one Object)? What is the use case for this method? disassemble - should I just implement this method to return a serializable form (e.g. String representation)? When and how is this method invoked? equals - is this for update? read? contention? dirty reads? What are the consequences of simply returning false in most cases? replace - I really don't understand where the three Object parameters come from, when this method is invoked, and what Hibernate expects to return, or how that return value is used. Any pointers would be appreciated. I've searched and read all I can find on the subject, but have not found much documentation at all explaining how these methods are used for mutable objects.

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• volatile vs. mutable in C++

  - by skydoor

  Hi I have a question about the difference between volatile and mutable. I noticed that both of the two means that it could be changed. What else? Are they the same thing? What's the difference? Where are they applicable? Why the two ideas are proposed? How to use them in different way? Thanks a lot.

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• Discovering a functional algorithm from a mutable one

  - by Garrett Rowe

  This isn't necessarily a Scala question, it's a design question that has to do with avoiding mutable state, functional thinking and that sort. It just happens that I'm using Scala. Given this set of requirements: Input comes from an essentially infinite stream of random numbers between 1 and 10 Final output is either SUCCEED or FAIL There can be multiple objects 'listening' to the stream at any particular time, and they can begin listening at different times so they all may have a different concept of the 'first' number; therefore listeners to the stream need to be decoupled from the stream itself. Pseudocode: if (first number == 1) SUCCEED else if (first number >= 9) FAIL else { first = first number rest = rest of stream for each (n in rest) { if (n == 1) FAIL else if (n == first) SUCCEED else continue } } Here is a possible mutable implementation: sealed trait Result case object Fail extends Result case object Succeed extends Result case object NoResult extends Result class StreamListener { private var target: Option[Int] = None def evaluate(n: Int): Result = target match { case None => if (n == 1) Succeed else if (n >= 9) Fail else { target = Some(n) NoResult } case Some(t) => if (n == t) Succeed else if (n == 1) Fail else NoResult } } This will work but smells to me. StreamListener.evaluate is not referentially transparent. And the use of the NoResult token just doesn't feel right. It does have the advantage though of being clear and easy to use/code. Besides there has to be a functional solution to this right? I've come up with 2 other possible options: Having evaluate return a (possibly new) StreamListener, but this means I would have to make Result a subtype of StreamListener which doesn't feel right. Letting evaluate take a Stream[Int] as a parameter and letting the StreamListener be in charge of consuming as much of the Stream as it needs to determine failure or success. The problem I see with this approach is that the class that registers the listeners should query each listener after each number is generated and take appropriate action immediately upon failure or success. With this approach, I don't see how that could happen since each listener is forcing evaluation of the Stream until it completes evaluation. There is no concept here of a single number generation. Is there any standard scala/fp idiom I'm overlooking here?

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• what's the different between a const version and mutable version member function

  - by Yongwei Xing

  Hi all I am very confused about the const version and mutable version member function like below:: value_type& top() { return this.item } const value_type& top() const { return this.item } What is the different these two functions? In what situation they would be used? Could someone give me some explanation about it? Best Regards,

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• Iterators for mutable collections in Scala?

  - by Lukasz Lew

  Does Scala have iterators with 'set' and 'remove' methods for iterating (and modifying) mutable collections like array? If there is no such iterator then is there a good reason for that?

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• unrecognized selector sent to instance while trying to add an object to a mutable array

  - by madpoet

  I'm following the "Your Second iOS App" and I decided to play with the code to understand Objective C well... What I'm trying to do is simply adding an object to a mutable array in a class. Here are the classes: BirdSighting.h #import <Foundation/Foundation.h> @interface BirdSighting : NSObject @property (nonatomic, copy) NSString *name; @property (nonatomic, copy) NSString *location; @property (nonatomic, copy) NSDate *date; -(id) initWithName: (NSString *) name location:(NSString *) location date:(NSDate *) date; @end BirdSighting.m #import "BirdSighting.h" @implementation BirdSighting -(id) initWithName:(NSString *)name location:(NSString *)location date:(NSDate *)date { self = [super init]; if(self) { _name = name; _location = location; _date = date; return self; } return nil; } @end BirdSightingDataController.h #import <Foundation/Foundation.h> @class BirdSighting; @interface BirdSightingDataController : NSObject @property (nonatomic, copy) NSMutableArray *masterBirdSightingList; - (NSUInteger) countOfList; - (BirdSighting *) objectInListAtIndex: (NSUInteger) theIndex; - (void) addBirdSightingWithSighting: (BirdSighting *) sighting; @end BirdSightingDataController.m #import "BirdSightingDataController.h" @implementation BirdSightingDataController - (id) init { if(self = [super init]) { NSMutableArray *sightingList = [[NSMutableArray alloc] init]; self.masterBirdSightingList = sightingList; return self; } return nil; } -(NSUInteger) countOfList { return [self.masterBirdSightingList count]; } - (BirdSighting *) objectInListAtIndex: (NSUInteger) theIndex { return [self.masterBirdSightingList objectAtIndex:theIndex]; } - (void) addBirdSightingWithSighting: (BirdSighting *) sighting { [self.masterBirdSightingList addObject:sighting]; } @end And this is where I'm trying to add a BirdSighting instance to the mutable array: #import "BirdsMasterViewController.h" #import "BirdsDetailViewController.h" #import "BirdSightingDataController.h" #import "BirdSighting.h" @implementation BirdsMasterViewController - (void)awakeFromNib { [super awakeFromNib]; BirdSightingDataController *dataController = [[BirdSightingDataController alloc] init]; NSDate *date = [NSDate date]; BirdSighting *sighting = [[[BirdSighting alloc] init] initWithName:@"Ebabil" location:@"Ankara" date: date]; [dataController addBirdSightingWithSighting: sighting]; NSLog(@"dataController: %@", dataController.masterBirdSightingList); self.dataController = dataController; } .......... @end It throws NSInvalidArgumentException in BirdSightingDataController addBirdSightingWithSighting method... What am I doing wrong?

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• search substring from mutable array in iphone

  - by user566431

  how to search substring from mutable array? NSMutableArrray names having string values, searchText is a substring to search from name array values. for (NSString *sTemp in names) { NSRange titleResultsRange = [sTemp rangeOfString:searchText options:NSCaseInsensitiveSearch]; //NSLog(@"sTemp = %@, searchText = %@",sTemp,searchText); NSLog(@"%@",titleResultsRange.length); if (titleResultsRange.length > 0) [Items addObject:sTemp]; }

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• How do I properly implement a property in F#?

  - by Greg D

  Consider my first attempt, a simple type in F# like the following: type Test() = inherit BaseImplementingNotifyPropertyChangedViaOnPropertyChanged() let mutable prop: string = null member this.Prop with public get() = prop and public set value = match value with | _ when value = prop -> () | _ -> let prop = value this.OnPropertyChanged("Prop") Now I test this via C# (this object is being exposed to a C# project, so apparent C# semantics are desirable): [TestMethod] public void TaskMaster_Test() { var target = new FTest(); string propName = null; target.PropertyChanged += (s, a) => propName = a.PropertyName; target.Prop = "newString"; Assert.AreEqual("Prop", propName); Assert.AreEqual("newString", target.Prop); return; } propName is properly assigned, my F# Setter is running, but the second assert is failing because the underlying value of prop isn't changed. This sort of makes sense to me, because if I remove mutable from the prop field, no error is generated (and one should be because I'm trying to mutate the value). I think I must be missing a fundamental concept. What's the correct way to rebind/mutate prop in the Test class so that I can pass my unit test?

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• Why does Microsoft advise against readonly fields with mutable values?

  - by Weeble

  In the Design Guidelines for Developing Class Libraries, Microsoft say: Do not assign instances of mutable types to read-only fields. The objects created using a mutable type can be modified after they are created. For example, arrays and most collections are mutable types while Int32, Uri, and String are immutable types. For fields that hold a mutable reference type, the read-only modifier prevents the field value from being overwritten but does not protect the mutable type from modification. This simply restates the behaviour of readonly without explaining why it's bad to use readonly. The implication appears to be that many people do not understand what "readonly" does and will wrongly expect readonly fields to be deeply immutable. In effect it advises using "readonly" as code documentation indicating deep immutability - despite the fact that the compiler has no way to enforce this - and disallows its use for its normal function: to ensure that the value of the field doesn't change after the object has been constructed. I feel uneasy with this recommendation to use "readonly" to indicate something other than its normal meaning understood by the compiler. I feel that it encourages people to misunderstand the meaning of "readonly", and furthermore to expect it to mean something that the author of the code might not intend. I feel that it precludes using it in places it could be useful - e.g. to show that some relationship between two mutable objects remains unchanged for the lifetime of one of those objects. The notion of assuming that readers do not understand the meaning of "readonly" also appears to be in contradiction to other advice from Microsoft, such as FxCop's "Do not initialize unnecessarily" rule, which assumes readers of your code to be experts in the language and should know that (for example) bool fields are automatically initialised to false, and stops you from providing the redundancy that shows "yes, this has been consciously set to false; I didn't just forget to initialize it". So, first and foremost, why do Microsoft advise against use of readonly for references to mutable types? I'd also be interested to know: Do you follow this Design Guideline in all your code? What do you expect when you see "readonly" in a piece of code you didn't write?

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• adding Json to mutable array resolves in crash

  - by user2957713

  Hello guys I am new to Xcode/iOS developing I trying to add json data to the mutable array , and it results in app crash :( so far here is my code: if(! [defaults objectForKey:@"Person1"]) [defaults setObject:[PersonsFromSearch objectAtIndex:index] forKey:@"Person1"]; else { NSMutableArray *Array = [[NSMutableArray alloc]init]; id object = [defaults objectForKey:@"Person1"]; Array = [object isKindOfClass:[NSArray class]] ? object : @[object]; [Array addObject:[PersonsFromSearch objectAtIndex:index]];//crash here :(( [Array moveObjectFromIndex:[Array count] toIndex:0]; } Crash Dump: * Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[__NSCFDictionary addObject:]: unrecognized selector sent to instance 0xbf98dc0' what is wrong here ? can you please help me to resolve this issue Array contains this (Json?) { Address = "\U05d3\U05e8\U05da \U05d4\U05e9\U05dc\U05d5\U05dd 53"; CellPhone = "052-3275381"; EMail = "[email protected]"; EnglishPerson = "Yehuda Konfortes"; FaceBookLink = ""; Fax1 = "03-7330703"; Fax2 = ""; FileNAme = "100050.jpg"; HomeEMail = ""; HomeFax = ""; HomePhone1 = ""; HomePhone2 = ""; PersonID = 100050; PersonName = "\U05d9\U05d4\U05d5\U05d3\U05d4 \U05e7\U05d5\U05e0\U05e4\U05d5\U05e8\U05d8\U05e1"; Phone1 = "03-7330733"; Phone2 = ""; ZipCode = ""; }

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• How do functional language gui bindings work?

  - by Roman A. Taycher

  Do they typically use non functional aspects of the language (including mutable variables). Are there other strategies? Could you describe them?

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• Why the good append syntax is so ugly, asks python newbie

  - by Cawas

  Now following my series of "python newbie questions" and based on another question. Go to http://python.net/~goodger/projects/pycon/2007/idiomatic/handout.html#other-languages-have-variables and scroll down to "Default Parameter Values". There you can find the following: def bad_append(new_item, a_list=[]): a_list.append(new_item) return a_list def good_append(new_item, a_list=None): if a_list is None: a_list = [] a_list.append(new_item) return a_list So, question here is: why is the "good" syntax over a known issue ugly like that in a programming language that promotes "elegant syntax" and "easy-to-use"? Why not just something in the definition itself, that the "argument" name is attached to a "localized" mutable object like: def better_append(new_item, a_list=[].local): a_list.append(new_item) return a_list I'm sure there would be a better way to do this syntax, but I'm also almost positive there's a good reason to why it hasn't been done. So, anyone happens to know why?

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• Force external function to be const

  - by vanna

  Here is my problem. I made a class with a member function declared as const that uses an external function that I cannot modify (declared in someone else's code) and that is not declared const. More precisely Someone else's code class B { public: void foo(); }; My code class A : public B { public: void bar() const { this->foo(); } }; I know that for member data we can force const-correctness by using mutable or const_cast. How can I 'hack' foo such that my compiler understands that I would like to use it as if it was const even if it is not declared in someone else's code ?

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• How to make an mutable C array for this data type?

  - by mystify

  There's this instance variable in my objective-c class: ALuint source; I need to have an mutable array of OpenAL Sources, so in this case probably I need a mutable C-array. But how would I create one? There are many questions regarding that: 1) How to create an mutable C-array? 2) How to add something to that mutable C-array? 3) How to remove something from that mutable C-array? 4) What memory management pitfalls must I be aware of? Must i free() it in my -dealloc method? And yes, I think this is something for the nice community wiki...

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• Project Euler 7 Scala Problem

  - by Nishu

  I was trying to solve Project Euler problem number 7 using scala 2.8 First solution implemented by me takes ~8 seconds def problem_7:Int = { var num = 17; var primes = new ArrayBuffer[Int](); primes += 2 primes += 3 primes += 5 primes += 7 primes += 11 primes += 13 while (primes.size < 10001){ if (isPrime(num, primes)) primes += num if (isPrime(num+2, primes)) primes += num+2 num += 6 } return primes.last; } def isPrime(num:Int, primes:ArrayBuffer[Int]):Boolean = { // if n == 2 return false; // if n == 3 return false; var r = Math.sqrt(num) for (i <- primes){ if(i <= r ){ if (num % i == 0) return false; } } return true; } Later I tried the same problem without storing prime numbers in array buffer. This take .118 seconds. def problem_7_alt:Int = { var limit = 10001; var count = 6; var num:Int = 17; while(count < limit){ if (isPrime2(num)) count += 1; if (isPrime2(num+2)) count += 1; num += 6; } return num; } def isPrime2(n:Int):Boolean = { // if n == 2 return false; // if n == 3 return false; var r = Math.sqrt(n) var f = 5; while (f <= r){ if (n % f == 0) { return false; } else if (n % (f+2) == 0) { return false; } f += 6; } return true; } I tried using various mutable array/list implementations in Scala but was not able to make solution one faster. I do not think that storing Int in a array of size 10001 can make program slow. Is there some better way to use lists/arrays in scala?

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• mutableCopyWithZone updating a property value.

  - by Jim

  I have a Class that I need to copy with the ability to make changes the value of a variable on both Classes. Simply put the classes need to remain clones of each other at all times. My understanding of the documentation is that I can do this using a shallow copy of the Class which has also been declared mutable. By shallow copying the pointer value for the variable will be cloned so that it is an exact match in both classes. So when I update the variable in the original the copy will be updated simultaneously. Is this right? As you can see below I have used mutableCopyWithZone in the class I want to copy. I have tried both NSCopyObject and allocWithZone methods to get this to work. Although I'm able to copy the class and it appears as intended, when updating the variable it is not changing value in the copied Class. - (id)mutableCopyWithZone:(NSZone *)zone { //ReviewViewer *copy = NSCopyObject(self, 0, zone); ReviewViewer *copy = [[[self class] allocWithZone:zone] init]; copy->infoTextViews = [infoTextViews copy]; return copy; } infoTextViews is a property declared as nonatomic, retain in the header file of the class being copied. I have also implemented the NSMutableCopying protocol accordingly. Any help would be great.

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• Java 1.4 singleton containing a mutable field

  - by Philippe

  Hi, I'm working on a legacy Java 1.4 project, and I have a factory that instantiates a csv file parser as a singleton. In my csv file parser, however, I have a HashSet that will store objects created from each line of my CSV file. All that will be used by a web application, and users will be uploading CSV files, possibly concurrently. Now my question is : what is the best way to prevent my list of objects to be modified by 2 users ? So far, I'm doing the following : final class MyParser { private File csvFile = null; private static Set myObjects = Collections.synchronizedSet(new HashSet); public synchronized void setFile(File file) { this.csvFile = file; } public void parse() FileReader fr = null; try { fr = new FileReader(csvFile); synchronized(myObjects) { myObjects.clear(); while(...) { // foreach line of my CSV, create a "MyObject" myObjects.add(new MyObject(...)); } } } catch (Exception e) { //... } } } Should I leave the lock only on the myObjects Set, or should I declare the whole parse() method as synchronized ? Also, how should I synchronize - both - the setting of the csvFile and the parsing ? I feel like my actual design is broken because threads could modify the csv file several times while a possibly long parse process is running. I hope I'm being clear enough, because myself am a bit confused on those multi-synchronization issues. Thanks ;-)

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• How to make a mutable ItemizedOverlay

  - by Hamy

  Hey all, I would like to make a Google map overlay with changable pins. An easy way to visualize this would be to think of a near real time overlay, where the pins are constantly changing location. However, I can't seem to think of a safe way to do this with the ItemizedOverlay. The problem seems to be the call to populate - If size() is called by some maps thread, and then my data changes, then the result when the maps call accesses getItem() can be an IndexOutOfBoundsException. Can anyone think of a better solution than overloading populate and wrapping super.populate in a synchronized block? Perhaps I could get better luck using a normal Overlay? The Itemized one seems to exist to manage the data for you, perhaps I am making a fundamental mistake by using it? Thanks for any help, my brain is hurting! Hamy

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• Is this technically thread safe despite being mutable?

  - by Finbarr

  Yes, the private member variable bar should be final right? But actually, in this instance, it is an atomic operation to simply read the value of an int. So is this technically thread safe? class foo { private int bar; public foo(int bar) { this.bar = bar; } public int getBar() { return bar; } } // assume infinite number of threads repeatedly calling getBar on the same instance of foo.

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• C# Dictionary<> and mutable keys

  - by Pierreten

  I was told that one of the many reasons strings were made immutable in the C# spec was to avoid the issue of HashTables having keys changed when references to the string keys altered their content. The Dictionary< type allows reference types to be used as a key. How does the dictionary avoid the issue of altered keys that lead to "misplaced" values? Is there a memberwise clone made of an object when used as a key?

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• Mutable objects and hashCode

  - by robert

  Have the following class: public class Member { private int x; private long y; private double d; public Member(int x, long y, double d) { this.x = x; this.y = y; this.d = d; } @Override public int hashCode() { final int prime = 31; int result = 1; result = prime * result + x; result = (int) (prime * result + y); result = (int) (prime * result + Double.doubleToLongBits(d)); return result; } @Override public boolean equals(Object obj) { if (this == obj) { return true; } if (obj instanceof Member) { Member other = (Member) obj; return other.x == x && other.y == y && Double.compare(d, other.d) == 0; } return false; } public static void main(String[] args) { Set<Member> test = new HashSet<Member>(); Member b = new Member(1, 2, 3); test.add(b); System.out.println(b.hashCode()); b.x = 0; System.out.println(b.hashCode()); Member first = test.iterator().next(); System.out.println(test.contains(first)); System.out.println(b.equals(first)); System.out.println(test.add(first)); } } It produces the following results: 30814 29853 false true true Because the hashCode depends of the state of the object it can no longer by retrieved properly, so the check for containment fails. The HashSet in no longer working properly. A solution would be to make Member immutable, but is that the only solution? Should all classes added to HashSets be immutable? Is there any other way to handle the situation? Regards.

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• Trouble accessing Mutable array

  - by Jared Gross

  Im having trouble with my for loop where I am trying to index user names. I am able to separate my original array into individual objects but am not able to send the value to a new array that I need to reference later on. The value and count for userNames in my self.userNamesArray = userNames; line is correct. But right after that when I log self.userNamesArray, I get (null). Any tips cause I'm not completely sure I'm cheers! .h @property (nonatomic, copy) NSMutableArray *userNamesArray; .m - (void)viewWillAppear:(BOOL)animated { self.friendsRelation = [[PFUser currentUser] objectForKey:@"friendsRelation"]; PFQuery *query = [self.friendsRelation query]; [query orderByAscending:@"username"]; [query findObjectsInBackgroundWithBlock:^(NSArray *objects, NSError *error) { if (error) { NSLog(@"Error: %@ %@", error, [error userInfo]); } else { self.friends = objects; NSArray *users = [self.friends valueForKey:@"username"]; NSLog(@"username:%@", users); //Create an array of name wrappers and pass to the root view controller. NSMutableArray *userNames = [[NSMutableArray alloc] initWithCapacity:[self.friends count]]; for (NSString *user in users) { componentsSeparatedByCharactersInSet:charSet]; NSArray *nameComponents = [user componentsSeparatedByString:@" "]; UserNameWrapper *userNameWrapper = [[UserNameWrapper alloc] initWithUserName:nil nameComponents:nameComponents]; [userNames addObject:userNameWrapper]; } self.userNamesArray = userNames; NSLog(@"userNamesArray:%@",self.userNamesArray); [self.tableView reloadData]; } Here's the code where I need to reference the self.userNamesArray where again, it is comping up nil. - (void)setUserNamesArray:(NSMutableArray *)newDataArray { if (newDataArray != self.userNamesArray) { self.userNamesArray = [newDataArray mutableCopy]; if (self.userNamesArray == nil) { self.sectionsArray = nil; NSLog(@"user names empty"); } else { [self configureSections]; } } }

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• Simple python oo issue

  - by Alex K

  Hello, Have a look a this simple example. I don't quite understand why o1 prints "Hello Alex" twice. I would think that because of the default self.a is always reset to the empty list. Could someone explain to me what's the rationale here? Thank you so much. class A(object): def __init__(self, a=[]): self.a = a o = A() o.a.append('Hello') o.a.append('Alex') print ' '.join(o.a) # >> prints Hello Alex o1 = A() o1.a.append('Hello') o1.a.append('Alex') print ' '.join(o1.a) # >> prints Hello Alex Hello Alex

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• Capturing Set Behavior with Mutating Elements

  - by Carl

  Using the Guava library, I have the following situation: SetMultimap<ImmutableFoo, Set<Foo>> setMM = HashMultimap.create(); Set<Foo> mask = Sets.newHashSet(); // ... some iteration construct { setMM.put(ImmutableFoo1, Sets.difference(SomeSetFoo1,mask)); setMM.put(ImmutableFoo1, Sets.difference(SomeSetFoo2,mask)); mask.add(someFoo); } that is, the same iteration to create the setMM is also used to create the mask - this can of course result in changes to hashCode()s and create duplicates within the SetMultimap backing. Ideally, I'd like the duplicates to drop without me having to make it happen, and avoid repeating the iteration to separately construct the multimap and mask. Any easy libraries/Set implementations to make that happen? Alternatively, can you identify a better way to drop the duplicates than: for (ImmutableFoo f : setMM.keySet()) setMM.putAll(f,setMM.removeAll(f)); revisiting the elements is probably not a performance problem, since I could combine a separate filter operation that needs to visit all the elements anyway.

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