The Core iOS Developer’s Cookbook, Fifth Edition

Boxing

Xcode 4.4 supports only literal scalar constants after the @. If you want to interpret a value and then convert it to a number object, you have to use the traditional method call:

Click here to view code image

NSNumber *two = [NSNumber numberWithInt:(1+1)];

Xcode 4.5 introduced boxed expression support, avoiding this awkward approach. Boxed expressions are values that are interpreted and then converted to number objects. A boxed expression is enclosed in parentheses, and it tells the compiler to evaluate and then convert to an object. For example:

NSNumber *two = @(1+1);

and

Click here to view code image

int foo = ...; // some value NSNumber *another = @(foo);

Boxed expressions are not limited to numbers. They work for strings as well. ...