Re[2]: Problem with +numberWithBool: ?

[Manuel Guesdon]

On Thu, 29 Jan 2004 13:12:30 +0000 Richard Frith-Macdonald <address@hidden> 
wrote:

 >| 
 >| On 29 Jan 2004, at 12:24, Manuel Guesdon wrote:
 >| 
 >| > Hi,
 >| >
 >| > +numberWithBool: is defined as:
 >| >
 >| >         + (NSNumber*) numberWithBool: (BOOL)value
 >| >         {
 >| >           if (value == YES)
 >| >             {
 >| >               return boolY;
 >| >             }
 >| >           else
 >| >             {
 >| >               return boolN;
 >| >             }
 >| >         }
 >| >
 >| > So as far as I understand [NSNumber numberWIthBool:2] will return 
 >| > boolN which is wrong as 2 is TRUE, isn't it ? (Or may
 >| > I need some sleep ? :-)
 >| 
 >| I agree it'll return boolN ... but 2 is not YES

But it's not NO either :-)


 >| Booleans in objc can be YES or NO ... 

No:
typedef unsigned char  BOOL;
#define YES   (BOOL)1
#define NO    (BOOL)0

So a BOOL can have a value between 0 and 255. 


 >| this is not the same thing as 
 >| true/false in C/ObjC conditionals where 0 is false and anything 
 >| non-zero is true.
 >| So ...
 >| 
 >| if (x)...
 >| is not the same as
 >| if (x == YES)
 >| where x is of type BOOL
 >| 
 >| which is why I prefer to write code which explicitly compares booleans 
 >| values with YES or NO.

I agree for NO comparaison but not on YES comparaison as I can imagine a lot of 
situations where programmer can make the
'mistake'.
For exemple: 
        o [NSNumber numberWithBool:strcmp(string1,string2)]
        o [NSNumber numberWithBoo:a!=b]
                For this one, could we be sure that (BOOL)(a!=b) will always 
return only 0 or 1 ? On all processors ?


 >| > I suggest:
 >| >         + (NSNumber*) numberWithBool: (BOOL)value
 >| >         {
 >| >           if (value == NO) // NO is always 0 but YES is a value != 0
 >| >             {
 >| >               return boolN;
 >| >             }
 >| >           else
 >| >             {
 >| >               return boolY;
 >| >             }
 >| >         }
 >| >
 >| 
 >| I think it might be better to raise an exception if value is not YES or 
 >| NO

Thinking of Objective-C as a langage over/derived from C, I can't agree: I 
think that for many (most of ?) developpers 0
is false/NO and true/YES is !(false/NO).

Manuel
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