CODEWITHSUNDEEP
iosobjective-carrays
3rdeye7
3rdeye7

Reputation: 536

Objective-C Array of object methods?

Im seeking some understanding on the code below:

     NSMutableArray<DEVICEID*>* device_a = @[

                                   [device_IDENTIFY command],
                                   [device_STATUS command],
                                   [device__POWER command]].mutableCopy;

Is this code creating an array of objects, where on each initialization of each element in the array calls the constructor for each object?

Upvotes: 1

Views: 491

Answers (3)

Lal Krishna
Lal Krishna

Reputation: 16160

According to Apple Docs

The NSMutableArray class declares the programmatic interface to objects that manage a modifiable array of objects. This class adds insertion and deletion operations to the basic array-handling behavior inherited from NSArray.

In the above code, I assume that command is a method which declared in an extension file of something(device_IDENTIFY's type) that returns an Object of type DEVICEID*.

ie., 

DEVICEID* identity = [device_IDENTIFY command];
DEVICEID* status= [device_STATUS command];
DEVICEID* identity = [device_POWER command];
NSArray *array = @[identity, status, identity]; //Created array with 3 DEVICEID* objects.
NSMutableArray<DEVICEID*>* device_a = [array mutableCopy]; //created mutable copy from An immutable one.

Upvotes: 0

CRD
CRD

Reputation: 53000

Is this code creating an array of objects,

Yes.

where on each initialization of each element in the array calls the constructor for each object?

It is not clear what you are asking here but maybe if the execution of the statement is explained you will have your answer.

When your statement is executed the steps are as follows:

  1. Each of the three method call expressions: [device_IDENTIFY command], [device_STATUS command] and [device__POWER command]; are evaluated. Each will return a reference to an object.
  2. Next the @[ ... ] is evaluated. This is Objective-C syntax to create an immutable array from the enclosed expressions. The result of this evaluation is a reference to a three element array, of type NSArray, containing the object references from step 1.
  3. Then the .mutableCopy method of NSArray is called on the array from step 2. This method returns a reference to a new mutable array, of type NSMutableArray.
  4. Finally the reference from step 3 is stored into the variable device_a.

The type of device_a is declared as NSMutableArray <DEVICEID *> *, this is an example of lightweight generics which were introduced into Objective-C to improve interfacing with Swift. A standard Objective-C mutable array, NSMutableArray, stores references to objects of any type. The <DEVICEID *> part of device_a's type declares that this array should only hold references to objects of type DEVICEID (or any of its subclasses), and Objective-C will perform compile time checks to enforce this in most (the "lightweight" part) cases.

HTH

Upvotes: 1

Dhiru
Dhiru

Reputation: 3060

A NSMutableArray is the array in Objective-c which can be modified at the rune time. obviously an array can hold any kind of object it is like . NSMutableArray<T> holds the generic object , sometimes we need to specify the array before allocating , which type of objects it should hold.

  NSMutableArray<DEVICEID*>* device_a;

The above code is used to specify, this will hold a pointer of deviceId object.

  @[[device_IDENTIFY command], [device_STATUS command], [device__POWER command]]

this will create and NSArray which is Immutable which can't be modified at run time so at last we mutable copy of NSArray the last line mutableCopy create a mutable copy .

I hope this will help you .

Upvotes: 1

Related Questions