Extracting common expressions

This next tip will sound obvious, but it will nicely introduce us to the next topic. Plus, it is a real problem frequently found in production code.

The ExtractCommonExpression demo creates a list box with a mere 1,000 entries, all in the form of author–title. A click on the Complicated expression button runs a short piece of code that reverses the order of author and title in the list box so that it shows entries in the form of title–author:

procedure TfrmCommonExpression.Button1Click(
  Sender: TObject);
var
  i: Integer;
  sw: TStopwatch;
begin
  ListBox1.Items.BeginUpdate;
  try
    sw := TStopwatch.StartNew;
    for i := 0 to ListBox1.Count - 1 do
      ListBox1.Items[i] :=
        Copy(ListBox1.Items[i], Pos('-', ListBox1.Items[i])
     ...