Question

I’m in WinForms and before saving changes to the DataBase, I had to check whether the used ErrorProvider holds an error for any of the displayed Controls.

I figured out several ways to do that among them:

• a simple foreach loop over the ControlContainer:

      foreach (Control c in ctrlcontainer)
      {
          if (epOrderHeader.GetError(c) != string.Empty)
          {
              return true;
          }
      }
      return false;
  

• Using the List extension Method Exists(Predicate):

  return (ctrlcontainer.Exists(c => epOrderHeader.GetError(c) != string.Empty);

Right from the stomache I expected the second to be the fastest, but using the Eqatec Profiler I discovered, that the foreach loop is slightly faster (in my case about 1ms). While this is insignificant, I still wonder why this happens?

How does the compiler translate these methods and why is the first one faster?

Answer 1

It is probably 1 ms slower in your case because List<T>.Exists calls FindIndex which is implemented in the following way:

public int FindIndex(int startIndex, int count, Predicate<T> match)
{
    if (startIndex > this._size)
    {
        ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.startIndex, ExceptionResource.ArgumentOutOfRange_Index);
    }
    if (count < 0 || startIndex > this._size - count)
    {
        ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.count, ExceptionResource.ArgumentOutOfRange_Count);
    }
    if (match == null)
    {
        ThrowHelper.ThrowArgumentNullException(ExceptionArgument.match);
    }
    int num = startIndex + count;
    for (int i = startIndex; i < num; i++)
    {
        if (match(this._items[i]))
        {
            return i;
        }
    }
    return -1;
}

So this is a little bit more than a simple foreach.