Best way to check if a Variable is nil?

Question

A common condition that all programs should do is to check if variables are assigned or not.

Take the below statements:

(1)

if Assigned(Ptr) then begin   // do something end; 

(2)

if Ptr <> nil then begin   // do something end; 

What is the difference between Assigned(Ptr) and Ptr <> nil?

Answer 1

It's usually the same... except when you check a function...

function mfi: TObject; begin   Result := nil; end;  procedure TForm1.btn1Click(Sender: TObject); type   TMyFunction = function: TObject of object; var   f: TMyFunction; begin   f := mfi;    if Assigned(f) then   begin     ShowMessage('yes'); // TRUE   end   else   begin     ShowMessage('no');   end;    if f <> nil then   begin     ShowMessage('yes');   end   else   begin     ShowMessage('no');  // FALSE   end; end; 

With the second syntax, it will check the result of the function, not the function itself...

Answer 2

As far as performance, there is no difference. I personally prefer the second form as I find that humans can parse the meaning quicker.