Why can't I create an NSMutableArray of integers?

Question

Is this format not allowed in Objective C?

NSMutableArray arrayA=[0,1,2,3,4,5];

is the only way to do this by adding one integer at a time?

Answer 1

There are two parts to this question:

Integers are value-types and NSMutableArray can only have object-types in it.

As another comment said, there's a magic syntax:

@1

Which says "I know this is a primitive, but please oh mighty compiler auto-magically make it an object for me."

Similarly, there's this syntax:

@[ ... ]

Which converts a C-array to an Objective-C NSArray [subclass].

So you could do this:

NSArray * array = @[ @1 , @2 , @3 , ... ] ;

Which would give you an array of numbers. You'd have to do this to use them though:

for ( NSNumber * number in array )
{
    NSLog ( @"This value is %i" , (int)number.intValue ) ;
    // Alternatively, which does the exact same thing:
    NSLog ( @"This value is %i" , (int)[number intValue] ) ;
}

If you wanted to make it mutable:

NSMutableArray * array = [ @[@1,@2,@3] mutableCopy ] ;

Other languages (like Python) have the syntax you want built-in because they are their own language and can internally represent anything as an object-type or value-type. They don't have to distinguish between them, and they pay the cost in terms of optimizability.

Objective-C is based on C and must still conform to C. Furthermore, the syntax must still conform to C, and number and [] tokens have specific meanings in C and C++ so they can't just re-define them. Therefore, they used their favorite syntax: the '@' sign, patterning it after strings.

char const * str = "abc" ;
NSString * str = @"abc" ;

int i = 1 ;
NSNumber * i = @1 ;

int arr[] = { 1 , 2 , 3 } ;
NSArray * arr = @[ @1 , @2 , @3 ] ;

// note: there's no concept of a dictionary in C
NSDictionary * dict = @{ @"a":@1 , @"b":@2 } ;

This is often called "boxing" because you're boxing up a primitive into an object.

Note that the inner part for a number doesn't necessarily have to be a literal:

int i = 5 ;
NSNumber * ii = @(i) ;

char const* str = "abc" ;
NSString * string = @(str) ;

See this for more information: http://clang.llvm.org/docs/ObjectiveCLiterals.html

Answer 2

You cannot do it because integers are primitives, and NSArray and NSMutableArray cannot store primitives. You can do it by using the literal syntax that creates NSNumbers:

NSMutableArray *arrayA=[@[@0,@1,@2,@3,@4,@5] mutableCopy];

Since the values inside the array are NSNumbers, you would need to unwrap them if you want to get integers by calling intValue on them.