CODEWITHSUNDEEP
iosobjective-cproperties
peco
peco

Reputation: 1451

Default values for primitive properties in Objective-C

I have an NSObject class, which has some primitive properties:

MyClass.h

@interface MyClass: NSObject

@property (nonatomic, assign) BOOL boolProp;
@property (nonatomic, assign) NSInteger intProp;

@end

MyClass.m

@implementation MyClass

// No init implemented

@end

From what I experienced, when there is no init method, then the properties default to "reasonable" values (BOOL to NO, intProp to 0). Is this defined behaviour? If yes, is there any Apple documentation for this behaviour?

Upvotes: 0

Views: 952

Answers (2)

Andrey Chernukha
Andrey Chernukha

Reputation: 21808

As for Apple documentation check Object Initialization. It mentions the topic raised in your question. For example

The default set-to-zero initialization performed on an instance variable during allocation is often sufficient

Upvotes: 5

Matic Oblak
Matic Oblak

Reputation: 16774

By default the structure behind the implementation (a C structure) is being set to 0 as a whole. Imagine using memset(self, 0, sizeof(_type)). All the rest is just typecasting. That means all pointers are Null, all integers or other numbers are 0, all boolean values are 0, NO or false.

I am not sure there is a documentation about it but if it is then it is on the level of allocation of NSObject. These defaults are there in general the way are described it but that might not actually meant they are guarantied. What I mean by that is that although this functionality of setting all to zero is working there is still a chance that this behaviour may not be true for some old version or for some future version. (unless this behaviour is in fact documented).

It should also be noted that as said the memory of structure itself is set to zero so no setters are being called to put things to zero and no logic is executed no matter how you setup your class.

Upvotes: 4

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