DELPHI: how to use “break” outside of loop or case?

Question

consider the following delphi pascal code:

var
  tc: TComponent
begin
{ do something to get tc }
repeat
  if(tc is TDBEdit)then begin
    if(check_something_about_edit(tc))then break;
    do_something_else_edit(tc);
    break;
  end else if(tc is TBMemo) then begin
    if(check_something_about_memo(tc))then break;
    do_something_else_memo(tc);
    break;
  end;
  raise exception.create('invalid component type');
until(true); {single iteration look required to use break }

I know there's probably some polymorphic stuff that I could do with TComponent, but that's not my question. I'm wondering if there's a way to get rid of the single iteration repeat-until statement. Without it, I can't use the break statement anywhere in the processing block, and I need that to stop processing at any time.

Answer 1

Pack it into a function and use exit to jump back. if there is more code to follow the repeat statement, use a local function/procedure, something like:

procedure ...
  procedure testsomething(tc: TComponent);
  begin 
    if(tc is TDBEdit)then begin
      if(check_something_about_edit(tc))then exit;
      do_something_else_edit(tc);
      exit;
    end else if(tc is TBMemo) then begin
      if(check_something_about_memo(tc))then exit;
      do_something_else_memo(tc);
      exit;
    end;
    raise exception.create('invalid component type');
  end;

var
  tc: TComponent;
begin
{ do something to get tc }
  try
    TestSomething(tc);
    { do something more }
  except
     ...
  end;
end;

Answer 2

There is another easy way to go:

if(tc is TDBEdit)then begin
  if not (check_something_about_edit(tc)) then
    do_something_else_edit(tc);
end else if(tc is TBMemo) then begin
  if not (check_something_about_memo(tc)) then
    do_something_else_memo(tc);
end else
  raise exception.create('invalid component type');
end;

Answer 3

What you are actually doing is using break as a goto. Ralph's suggestion to use a function as a scope is a good one. But otherwise you might as well be honest and use a 'goto finished'. Losing the repeat will make it actually more readable.

Answer 4

Why do you want to use break rather than Exit? Break in Delphi is not the same as "break" in the curly brace languages.

var
  tc: TComponent
begin
  { do something to get tc }
  if (tc is TDBEdit) then 
  begin
    if not (check_something_about_edit(tc)) then 
      do_something_else_edit(tc);
    Exit;
  end;
  if (tc is TBMemo) then 
  begin
    if not (check_something_about_memo(tc)) then 
      do_something_else_memo(tc);
    Exit;
  end;
  raise exception.create('invalid component type');
end;

A point about layout. If you didn't try to reduce whitespace so much it mightn't take "another hour to make sure all my if-else's lined up correctly" as you said in an earlier comment.

If you have code that you want to execute after this, either use Ralph's suggestion of a local procedure, or wrap in a try..finally - the code in the finally will still be executed.