Bug1

BrowseOverflow/Question.m

@@ -33,5 +33,16 @@ - (NSArray *)answers {
     return [[answerSet allObjects] sortedArrayUsingSelector: @selector(compare:)];
 }
 
+- (BOOL)isEqual:(id)object {
+    if ([object isKindOfClass: [Question class]]) {
+        Question *other = (Question *)object;
+        return (self.questionID == other.questionID);
+    } else {
+        return [super isEqual: object];
+    }
+}
 
+- (NSUInteger)hash {
+    return (NSUInteger)self.questionID;
+}
 @end

BrowseOverflow/Topic.h

@@ -12,9 +12,7 @@
 /**
  * A class representing a particular subject on Stack Overflow.
  */
-@interface Topic : NSObject {
-    NSArray *questions;
-}
+@interface Topic : NSObject
 /**
  * A name for this topic, suitable for displaying in the UI.
  */

BrowseOverflow/Topic.m

@@ -16,30 +16,34 @@ - (NSArray *)sortQuestionsLatestFirst: (NSArray *)questionList;
 @end
 
 @implementation Topic
+{
+    NSSet *questions;
+}
 @synthesize name;
 @synthesize tag;
 
 - (id)initWithName:(NSString *)newName tag: (NSString *)newTag {
     if ((self = [super init])) {
         name = [newName copy];
         tag = [newTag copy];
-        questions = [[NSArray alloc] init];
+        questions = [[NSSet alloc] init];
     }
     return self;
 }
 
 
 - (void)addQuestion: (Question *)question {
-    NSArray *newQuestions = [questions arrayByAddingObject: question];
+    NSSet *newQuestions = [questions setByAddingObject: question];
+    NSArray *latestQuestions = [newQuestions allObjects];
     if ([newQuestions count] > 20) {
-        newQuestions = [self sortQuestionsLatestFirst: newQuestions];
-        newQuestions = [newQuestions subarrayWithRange: NSMakeRange(0, 20)];
+        latestQuestions = [self sortQuestionsLatestFirst: latestQuestions];
+        latestQuestions = [latestQuestions subarrayWithRange: NSMakeRange(0, 20)];
     }
-    questions = newQuestions;
+    questions = [NSSet setWithArray: latestQuestions];
 }
 
 - (NSArray *)recentQuestions {
-    return [self sortQuestionsLatestFirst: questions];
+    return [self sortQuestionsLatestFirst: [questions allObjects]];
 }
 
 - (NSArray *)sortQuestionsLatestFirst: (NSArray *)questionList {

BrowseOverflowTests/QuestionListTableDataSourceTests.m

@@ -39,8 +39,10 @@ - (void)setUp {
     firstCell = [NSIndexPath indexPathForRow: 0 inSection: 0];
     question1 = [[Question alloc] init];
     question1.title = @"Question One";
+    question1.questionID = 1;
     question1.score = 2;
     question2 = [[Question alloc] init];
+    question2.questionID = 2;
     question2.title = @"Question Two";
 
     asker1 = [[Person alloc] initWithName: @"Graham Lee" avatarLocation: @"http://www.gravatar.com/avatar/563290c0c1b776a315b36e863b388a0c"];

BrowseOverflowTests/TopicTests.m

@@ -11,9 +11,14 @@
 #import "Question.h"
 
 @implementation TopicTests
+{
+    Question *questionWithID123;
+}
 
 - (void)setUp {
     topic = [[Topic alloc] initWithName: @"iPhone" tag: @"iphone"];
+    questionWithID123 = [[Question alloc] init];
+    questionWithID123.questionID = 123;
 }
 
 - (void)tearDown {
@@ -40,16 +45,17 @@ - (void)testForInitiallyEmptyQuestionList {
 }
 
 - (void)testAddingAQuestionToTheList {
-    Question *question = [[Question alloc] init];
-    [topic addQuestion: question];
+    [topic addQuestion: questionWithID123];
     STAssertEquals([[topic recentQuestions] count], (NSUInteger)1, @"Add a question, and the count of questions should go up");
 }
 
 - (void)testQuestionsAreListedChronologically {
     Question *q1 = [[Question alloc] init];
+    q1.questionID = 1;
     q1.date = [NSDate distantPast];
 
     Question *q2 = [[Question alloc] init];
+    q2.questionID = 2;
     q2.date = [NSDate distantFuture];
 
     [topic addQuestion: q1];
@@ -63,11 +69,26 @@ - (void)testQuestionsAreListedChronologically {
 }
 
 - (void)testLimitOfTwentyQuestions {
-    Question *q1 = [[Question alloc] init];
     for (NSInteger i = 0; i < 25; i++) {
-        [topic addQuestion: q1];
+        Question *q = [[Question alloc] init];
+        q.questionID = i;
+        [topic addQuestion: q];
     }
     STAssertTrue([[topic recentQuestions] count] < 21, @"There should never be more than twenty questions");
 }
 
+- (void)testThatTheSameQuestionCannotBeAddedTwiceToTheList {
+    for (NSInteger i = 0; i < 2; i++) {
+        [topic addQuestion: questionWithID123];
+    }
+    STAssertEquals([[topic recentQuestions] count], (NSUInteger)1, @"Adding the same question twice should only yield one entry");
+}
+
+- (void)testThatDifferentQuestionsWithTheSameValueCannotBothBeInTheList {
+    Question *alsoQ123 = [[Question alloc] init];
+    alsoQ123.questionID = 123;
+    [topic addQuestion: questionWithID123];
+    [topic addQuestion: alsoQ123];
+    STAssertEquals([[topic recentQuestions] count], (NSUInteger)1, @"Adding questions with the same value should only yield one entry");
+}
 @end