delphi - 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...