objective c - Why would CFRelease(NULL) crash?

Question

Is there a reason why CFRelease does not check for NULL? Isn't it unacceptable when [nil release]; free(NULL); delete NULL; all work perfectly fine?

Answer 1

The source code to CoreFoundation is publicly available. Specifically, for Snow Leopard the code to CFRelease is in http://www.opensource.apple.com/source/CF/CF-550/CFRuntime.c

Here is what the relevant portion looks like:

void CFRelease(CFTypeRef cf) {
    if (NULL == cf) HALT;
#if DEPLOYMENT_TARGET_MACOSX || DEPLOYMENT_TARGET_EMBEDDED
    if (CF_IS_COLLECTABLE(cf)) {
        if (CFTYPE_IS_OBJC(cf)) {
            // release the GC-visible reference.
            auto_zone_release(auto_zone(), (void*)cf);
        } else {
            // special-case CF objects for better performance.
            _CFRelease(cf);
        }
        return;
    }
#endif
}

This doesn't answer your question about design motivations, but you also asked why CFRelease does not check for NULL. It does check, and fails on purpose when NULL is passed as the parameter.

My personal belief is similar to Quinn's- that the CF designers felt it is a programming error to pass NULL.