Why are Delphi objects assigned even after calling .Free?

Question

In Delphi, why does the Assigned() function still return True after I call the destructor?

The below example code will write \"sl is still assigned\" to the console.

Answer 1

The Free method of TObject is like the "delete operator" in C++. Calling free will first call the Destroy function and then it will free the memory block that was allocated for the object. By default the pointer to the memory is not then set to zero because this will use up one instruction.

The correct thing to do in most cases is not to set the pointer to zero because in most cases it does not matter. However, sometimes it is important and so you should only nil the pointer for those cases.

For example. In a function where an object is created and then freed at the end of the function there is no point in setting the variable to zero since that is just wasting cpu time.

But for a global object or field that might be referenced again later you should set it to zero. Use FreeAndNil or just set the pointer to nil yourself, does not matter. But stay away from zeroing variables that do not need to be zeroed by default.