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copied!<p>I consider this case as being described in the link you provided:</p> <blockquote> <p>Boxing a value of enum type will result in a NSNumber pointer with a creation method according to the underlying type of the enum, which can be a fixed underlying type or a compiler-defined integer type capable of representing the values of all the members of the enumeration:</p> <pre><code>typedef enum : unsigned char { Red, Green, Blue } Color; Color col => Red; NSNumber *nsCol = @(col); // => [NSNumber numberWithUnsignedChar:] </code></pre> </blockquote> <p>but the details of the promotions in the libraries are not covered, and that is where the difference in expectations is introduced.</p> <p><code>-testA</code> ends up calling <code>+[NSNumber numberWithInt:]</code></p> <p><code>-testB</code> ends up calling <code>+[NSNumber numberWithUnsignedInt:]</code></p> <p>So the abstracted 'promotion' you see is because <code>CFNumber</code> (and consequently <code>NSNumber</code>) do not actually support unsigned values at this time (see constants of <code>CFNumberType</code> enums) -- based on the output you are seeing, one would then assume <code>NSNumber</code> implementations simply promote to the next signed type capable of representing all values in the case of an unsigned initializer of constructor -- apparently without testing the value to see if any 'width minimization' can be applied.</p> <p>Of course, <code>NSNumber</code> declares constructors and initializers which take unsigned types as parameters, but the internal representation of an unsigned integer is actually stored as a signed integer representation.</p> <p>The compiler appears to call appropriate/exact convenience constructors when promoting the boxed literal to an <code>NSNumber</code>. For example a <code>uint16_t</code> typed enum will be stored as a 32 bit int (via <code>numberWithUnsignedShort:</code>), and a int32_t is also a 32 bit int (via <code>numberWithInt:</code>). Although, in the case of <code>-testA</code> the value is also known, so a more appropriate constructor could also be called there -- so the compiler is only width-minimizing based on type, not type and value. when the type of an enum is unspecified or specified as an unsigned type, then you may see promotions like this.</p>

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