ios - Declaration under interface in Objective C -


i studying big nerd ranch's objective c programming book. saw code below:

@interface bnremployee : bnrperson {     nsmutablearray *_assets; }   @property (nonatomic) unsigned int employeeid; @property (nonatomic) unsigned int officealarmcode; @property (nonatomic) nsdate *hiredate; @property (nonatomic, copy) nsarray *assets;  -(double)yearsofemployment; -(void)addasset:(bnrasset *)a; -(unsigned int)valueofassets;

in code, why declare nsmutablearray *_assets under interface? how different declaring property, , purpose serve?

lastly, see there nsarray *assets in property. same nsmutablearray *_assets?

i'm not sure why did general practice, shouldn't yourself. header file should reserved public interface of class. put things in there callers , users of class need see, properties, methods, , perhaps extern constants.

then question becomes in implementation whether use property or regular instance variable. largely preference based. people declare properties , don't use plain ivars @ all. others use ivars , properties when want declare custom setter/getter variable in question. in latter camp arguable clearer , easier read if property.

edit

i misread code. above stands normally, doing there exposing api different underlying data. editing answer now.

when declare property without custom @synthesize , without having overridden both setter , getter if applicable, underlying variable created underscore in front. doing here returning nsarray in public api ensure internal variable not modified while internally using nsmutablearray.

i in general though, variable declaration (nsmutablearray *_assets;) should still go in implementation file. caller should not need know mutable under hood.

there lot of existing questions touching upon already. here search query number of them: https://stackoverflow.com/search?q=mutable+ivar+immutable+property


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