Question

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Synthesized property and variable with underscore prefix: what does this mean?

I’ve seen both of these in code; what’s the difference?

@synthesize fooBar;

@synthesize fooBar=_fooBar;

Answer 1

@synthesize fooBar; creates accessors for the property fooBar using an instance variable with the same name for storage, while the =_fooBar tells the compiler to use the instance variable named _fooBar as storage instead. You don’t need to use the =... if you have your instance variables and properties identically named, and you do otherwise.