Charles Panel Charles Panel - 5 months ago 25
Objective-C Question

Objective-C: Curly braces after variable declaration

I'm trying to get a better understanding of good Objective-C/Swift practices, and I am currently reading this: https://github.com/facebook/pop/blob/master/pop/POPAnimatableProperty.mm , from the Awesome-iOS repo in GitHub. I don't understand these two bits of code.

1/

static POPStaticAnimatablePropertyState _staticStates[] =
{
/* CALayer */

{kPOPLayerBackgroundColor,
^(CALayer *obj, CGFloat values[]) {
POPCGColorGetRGBAComponents(obj.backgroundColor, values);
},
^(CALayer *obj, const CGFloat values[]) {
CGColorRef color = POPCGColorRGBACreate(values);
[obj setBackgroundColor:color];
CGColorRelease(color);
},
kPOPThresholdColor
},

{kPOPLayerBounds,
^(CALayer *obj, CGFloat values[]) {
values_from_rect(values, [obj bounds]);
},
^(CALayer *obj, const CGFloat values[]) {
[obj setBounds:values_to_rect(values)];
},
kPOPThresholdPoint
},
...
}


I get the block part, that is:

^(CALayer *obj, CGFloat values[]) {
POPCGColorGetRGBAComponents(obj.backgroundColor, values);
}


What I don't get is the two curly braces right after

static POPStaticAnimatablePropertyState _staticStates[] =


What is it supposed to be?

2/Similar, but not identical, this piece of code:

static NSUInteger staticIndexWithName(NSString *aName)
{
NSUInteger idx = 0;

while (idx < POP_ARRAY_COUNT(_staticStates)) {
if ([_staticStates[idx].name isEqualToString:aName])
return idx;
idx++;
}

return NSNotFound;
}


It seems to be a block of code after a variable declaration. Is it supposed to execute everytime the variable is used?

Answer

First one is declaring an array of POPStaticAnimatablePropertyState statically. It seems that POPStaticAnimatablePropertyState is a struct itself (possibly via typedef) which has a number, a block, another block, and another number.

Second one is just a static C function, nothing special there.

This code is not a good Objective-C/Swift practice. It's just regular plain C, possibly written to be easily ported or written in this way for pure performance.

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