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    /*
     If you run loadThumbnail() in an *iPhone-only app that is installed on the iPad*,
     the Photos framework will callback first with a degraded version of the requested asset image,
     and then it will callback a second time with a nil image. 
     
     If you're not careful and you pass the nil image to your UIImageView, then you will never see the thumbnail.
     The UIImageView will first get set with a proper UIImage, then soon after with a nil UIImage.
     The solution is to ignore or discard any image that is nil.
     
     So what happens if you try to setup PHImageRequestOptions to make sure that Photos framework only calls back once?

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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 {