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Re: IsNullInstance() for Callback [message #1659 is a reply to message #1656]

Sat, 11 March 2006 20:54

hojtsy
Messages: 241
Registered: January 2006
Location: Budapest, Hungary

Experienced Member

I see the analogy. But I would write that code differently.

typedef void (*VoidFunctionPointer)();
VoidFunctionPointer operationPointer = NULL;
...........
if(NULL == operationPointer) {
}

This version is longer and but readers have a chance of understanding what the if() does withouth seeing the definition of the pointer variable, which could be pages away or in a different file. With this descriptive coding style code comments could be shorter, but yes I would put comments around any function pointer usage if the code is to be read by anyone else than myself. This area is not that well understood by the avarage programmers.
Now let's see how can I turn back this analogy to Callback. The best version I could come up with is:

Callback operationCallback;
...........
if((bool) operationCallback) {

I know that (bool) is unnecessary, but implicit conversions just make the situation less understandable for average programmers. With seeing just the if line some of them will start to think that operationCallback is bool, or maybe int. This way I can convey the info that operationCallback is not bool, and they should go and check it's type. But it is still quite cryptic. The best notation would be something which could be read aloud as it's own explanation. Such notation is:

if(operationCallback.IsValid()) {

Now try to read out aloud this one, and then the one without IsValid.
Adding this one method will only have minimal effect on the readablity of a big application, so its not that important. I just wanted to explain my point of view.

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