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SecRequestSharedWebCredential(nil, nil) { credentials, error in
    guard error == nil else {
        let cocoaError = error! as NSError
        let errorIsExpected = cocoaError.domain == NSOSStatusErrorDomain && cocoaError.code == Int(errSecItemNotFound)
        
        if !errorIsExpected {
            // Do something with an unexpected error.
        }
        
        return

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// Presentation Layer Hit Test
// Source: WWDC2014 Session 236
- (UIView *)hitTest:(CGPoint)point withEvent:(UIEvent *)event
{
    CGPoint pointInSuperview = [self convertPoint:point toView:self.superview];
    CGPoint presentationLayerPoint = [self.layer.presentationLayer convertPoint:pointInSuperview fromLayer:self.superview.layer];
    return [super hitTest:presentationLayerPoint withEvent:event];
}

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/**
 Provides the ability to verify key paths at compile time.
 
 If "keyPath" does not exist, a compile-time error will be generated.
 
 Example:
    // Verifies "isFinished" exists on "operation".
    NSString *key = SQKeyPath(operation, isFinished);
 
    // Verifies "isFinished" exists on self.

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- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{    
    UITableViewCell *cell =
        [tableView dequeueReusableCellWithIdentifier:REUSABLE_CELL_ID];

    UILabel *label = (UILabel *)[cell viewWithTag:VIEW_TAG];
    Model *someModel = [self getModelFromIndexPath:indexPath];
    
    //  `takeUntil:` makes the RACObserve() signal complete (and thus breaks the subscription)
    //  when the cell is recycled.

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// Source: WWDC 2013 Session 228

CFMutableStringRef string = (__bridgeCFMutableStringRef)[@"Hello!こんにちは!สวสัดี!مرحبا!您好!" mutableCopy];

CFStringTransform(string, NULL, kCFStringTransformToLatin, NO);
// Hello! kon'nichiha! swạsdī! mrḥbạ! nín hǎo!

CFStringTransform(string, NULL, kCFStringTransformStripCombiningMarks, NO);
// Hello! kon'nichiha! swasdi! mrhba! nin hao!

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/*
Extract date from natural language string
Source: WWDC2012 Session 215 - Text and Linguistic Analysis
*/

NSDataDetector *dateDetector = [NSDataDetector dataDetectorWithTypes:NSTextCheckingTypeDate error:nil];
NSString *dateString = @"13th September 1986 11:59pm";
NSTextCheckingResult *result = [dateDetector firstMatchInString:dateString
                                                        options:0
                                                          range:NSMakeRange(0, [dateString length])];

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// Source: WWDC 2012 Session 216
// Advanced Appearance Customization on iOS
// Rather useful when your button is smaller than the golden 44 points

- (BOOL)pointInside:(CGPoint)point withEvent:(UIEvent *)event
{
    CGFloat widthDelta = 44.0 - bounds.size.width;
    CGFloat heightDelta = 44.0 - bounds.size.height;
    CGRect bounds = CGRectInset(self.bounds, -0.5 * widthDelta, -0.5 * heightDelta);
    return CGRectContainsPoint(bounds, point);

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NSNumber *value;
value = @'X';       // char
value = @12345      // int
value = @12345ul    // unsigned long
value = @12345ll    // long long
value = @123.45f    // float
value = @123.45     // double
value = @YES        // BOOL

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/*
 Source: WWDC2012 Modern Objective-C talk
 How to get a constant literal container to work.
*/

@implementation MyClass

static NSArray *thePlanets;

+ (void)initialize {

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/*
 Source: Building Concurrent User Interfaces on iOS
 WWDC2012 Session 211 by Andy Matuschak
*/

NSOperationQueue *queue = [[NSOperation alloc] init];
NSBlockOperation *op = [[NSBlockOperation alloc] init];
__weak NSBlockOperation *weakOp = op;
[op addExecutionBlock:^{
    for (int i = 0; i < 10000; i++) {