Auto Boxing of primitives

Question

I can't seem to figure out how to get Objective-c to auto box my primitives.

I assumed that i would be able to do the following

float foo = 12.5f;
NSNumber* bar;

bar = foo;

However i find that i have used to the more verbose method of

float foo = 12.5f;
NSNumber* bar;

bar = [NSNumber numberWithFloat:foo];

Am i doing it wrong or is this as good as it gets?

Answer 1

Unfortunately, Objective-C does not do auto-boxing or unboxing of primitive types to NSNumber. When put that way, it may be clear why: Objective-C has no concept of NSNumber, a class in the Cocoa Foundation framework. As a small superset of C, Objective-C doesn't have a "native" numeric object type--just the native C types.

Edit Aug 2012 As of Xcode 4.4 (and LLVM 4.0), you can now use some syntactic sugar to wrap numbers. Following your example, these "boxed expressions" now work:

float foo = 12.5f;
NSNumber* bar;

bar = @(foo);
bar = @12.5f;

Answer 2

Clang 3.1 and Apple LLVM 4.0 (included in Xcode 4.4) support a new boxing feature: http://clang.llvm.org/docs/ObjectiveCLiterals.html#objc_boxed_expressions

You're now able to write:

NSNumber *bar = @(foo);

as well as:

NSNumber *bar = @12.5F;

So it just got a little better. :)