delphi - How to detect "dangling pointers" if "Assigned()" can't do it?

Question

In another question, I found out that the Assigned() function is identical to Pointer <> nil. It has always been my understanding that Assigned() was detecting these dangling pointers, but now I've learned it does not. Dangling Pointers are those which may have been created at one point, but have since been free'd and haven't been assigned to nil yet.

If Assigned() can't detect dangling pointers, then what can? I'd like to check my object to make sure it's really a valid created object before I try to work with it. I don't use FreeAndNil as many recommend, because I like to be direct. I just use SomeObject.Free.

Access Violations are my worst enemy - I do all I can to prevent their appearance.

Answer 1

If you have an object variable in scope and it may or may not be a valid reference, FreeAndNil is what you should be using. That or fixing your code so that your object references are more tightly managed so it's never a question.

Access Violations shouldn't be thought of as an enemy. They're bugs: they mean you made a mistake that needs fixed. (Or that there's a bug in some code you're relying on, but I find most often that I'm the one who screwed up, especially when dealing with the RTL, VCL, or Win32 API.)