CODEWITHSUNDEEP
objective-cc++11types
Pépito
Pépito

Reputation: 57

Is Objective-C's id like auto in C++11?

In code like

- (void)driveFromOrigin:(id)theOrigin toDestination:(id)theDestination;
- (id)initWithModel:(NSString *)aModel;

does id allow me to specify a type?

Upvotes: 0

Views: 1433

Answers (3)

user49354
user49354

Reputation: 199

Yes, in xcode8, you can use __auto_type

Upvotes: 1

gnasher729
gnasher729

Reputation: 52538

id is similar to "void*". It means "pointer to any kind of Objective-C instance". So unlike a void*, it is under ARC control. It can be assigned to any variable of type "pointer to Objective-C object" and vice versa.

Using variables of type "id" has the disadvantage that the compiler has no idea what kind of object you have, so it will allow you to send messages to it, even if it doesn't understand them. 

NSString* aString = @"Hello";
NSUInteger count = aString.count; // Doesn't compile because the compiler knows it's wrong
id bString = aString; // It's a string, but the compiler doesn't know. 
count = bString.count; // Compiles but throws exception at runtime.

"auto" in C++ is different. It determines the correct type from the argument on the right hand side. So the variable is fully declared except that the compiler provided the type and not you.

PS. "init" methods should return "instancetype" and not id. "instancetype" is kind of, roughly, similar to "auto".

Upvotes: 3

Michał Banasiak
Michał Banasiak

Reputation: 960

not exactly. id means objective-c object type. compiler wouldn't know its type during compilatrion. auto instructs the compiler to inference variable type.

Upvotes: 0

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