Question

I can’t count how many times I may have erroneously done this:

for  i := 0 to MyList.count-1 do begin
  myobject := TMyObject(MyList[i])
  .......
end;

when it should be this:

for  i := 0 to MyList.count-1 do begin
  myobject := TMyObject(MyList.objects[i])
  .......
end;

Note the objects in the second snippet of code.

The erroneous snippet of code will run, and will obviously throw an access violation when I try to make use of myobject. But it isn’t always apparent what it is I am doing wrong.

Is there a compiler option which will guard against this?

Answer 1

Delphi has 2 ways to typecast, hardcast using TObject(var) and a softcast using the As operator.
It is a good practice to always use the As operator unless you are 100% sure.
In your specific example

(MyList[i]) as TMyObject does not compile
where as

(MyList.objects[i]) as TMyObject does.