Question

I would like to know if the following code may ever fail with the access violation or if it’s safe. Is the first member of the statement with AND operator always checked as first or may be (by some compiler optimization or something) checked the second one as first ?

var
  Item: TSomething;

procedure DoSomething;
begin
  if Assigned(Item) and (Item.SomeProperty) then
    DoSomethingElse;
end;

Is the code above definitely safe ?

Thanks!

Answer 1

The code is safe given boolean short-circuit evaluation is active:

In the {$B-} state, the compiler generates code for short-circuit Boolean expression evaluation, which means that evaluation stops as soon as the result of the entire expression becomes evident in left to right order of evaluation.

It is a bit confusing as the B (or BOOLEVAL with long name) directive must be turned OFF to switch short-circuit evaluation ON…

See also Operator Precedence.