macOS what do ~ and -> mean/do?

[MrFusion]

I am going through Apple's AnimatedTableView example.
It contains some code I haven't seen before, and I was wondering how this is working.

The ATColorCell.m file contains this code:

- (id)copyWithZone:(NSZone *)zone 
{
    self = [super copyWithZone:zone];
   [COLOR="Blue"] self->_color = [_color retain];[/COLOR] //??? 
    return self;
}

- (NSUInteger)hitTestForEvent:(NSEvent *)event inRect:(NSRect)frame ofView:(NSView *)controlView {
    NSPoint point = [controlView convertPoint:[event locationInWindow] fromView:nil];
    NSRect colorRect = [self colorRectForFrame:frame];
    if (NSPointInRect(point, colorRect)) {
        // We combine in our own hit test marker
        return NSCellHitTrackableArea | ATCellHitTestColorRect;
    } else {
        NSUInteger result = [super hitTestForEvent:event inRect:[self _titleFrameForInteriorFrame:frame] ofView:controlView];
        // We don't want the label to be editable
        [COLOR="Blue"]result = result & ~NSCellHitEditableTextArea; [/COLOR]//??? ~ is negate in math
        return result;
    }   
}

Why not do or something similar?

 (id)copyWithZone:(NSZone *)zone 
{
    id newobject = [super copyWithZone:zone];
    [newobject setColor:[self color]]; 
    return newobject;
}

 

[gnasher729]

I am going through Apple's AnimatedTableView example.
It contains some code I haven't seen before, and I was wondering how this is working.

http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1256.pdf

is the latest version of the C Standard which will explain what ~ and -> do.

 

[subsonix]

The tilde ~ is a bitwise NOT, so paired with the AND it will store the result in the result variable in the example.

http://en.wikipedia.org/wiki/Bitwise_operation#NOT

-> is used to reach struct members from a pointer to struct in C, and since valid C is valid Obj C, that is what this is.

 

[Guiyon]

In addition to being the indirect struct member operator in C, the '->' operator, when used inside Objective-C object, allows direct access to the instance variables. For example:

@interface SomeClass : NSObject
@property (readonly) UIColor *color;
@end

@implementation SomeClass
@synthesize color = _color;

- (void)someMethod
{
    // Directly accesses the _color instance variable instead of
    // going through the mutator/accessor method
    self->_color = [[UIColor redColor] retain];

    NSLog(@"%@",[self->_color description]);

    [self->_color release], self->_color = nil;
}
@end

 

[subsonix]

Yes, and that tells something about what an Obj C object actuall is. Dereferencing self and then use a the dot syntax should work equally well i.e: (*self)._color