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Most languages use the true/false keywords for boolean values. I found that even Smalltalk is using true/false. I know Objective-C is just borrowing concepts from Smalltalk, not the language itself, but I’m curious why it’s using YES/NO instead of the more widely-used true/false. Is there any historical reason?
Objective-C was designed to be (and still is) a strict superset of C. The creators worked very hard to ensure that they did not break compatibility with C in any way. They also tried to make their modifications somewhat obvious so that it would be easy to tell which parts of the code use Objective-C and which parts use plain C. Case in point, the
@used to denote NSStrings rather than just using quotes. This allows plain C strings to coexist with the new ones.C already had an informal system of TRUE/FALSE macros. I suspect the designers of Objective-C chose the YES/NO macros to avoid conflict and to make it obvious that the code is actually Objective-C. Notice also the usage
nilfor the ’empty’ object rather than just modifying the behavior of good old NULL.