Question

Below is the code i am using

private void TestFunction()
{
  foreach (MySampleClass c in dictSampleClass)
  {
    String sText = c.VAR1 + c.VAR2 + c.VAR3
    PerformSomeTask(sText,c.VAR4);
  }
}

My friend has suggesed to change to (to improve performance. dictSampleClass is a dictionary. It has 10K objects)

private void TestFunction()
{
  String sText="";
  foreach (MySampleClass c in dictSampleClass)
  {
    sText = c.VAR1 + c.VAR2 + c.VAR3
    PerformSomeTask(sText,c.VAR4);
  }
}

My Question is, “Does above change improve performance? if yes, how?”

WOW thats more than expected response. Most guys said “C# compiler would take care of that”. So what about c compiler??

Answer 1

The compiler has intelligence to move variable declarations into/out of loops where required. In your example however, you are using a string, which is immutable. By declaring it outside I believe you are trying to “create once, use many”, however strings are created each time they are modified so you can’t achieve that.

Not to sound harse, but this is a premature optimisation, and likely a failing one – due to string immutability.

If the collection is large, go down the route of appending many strings into a StringBuilder – separated by a delimiter. Then split the string on this delimiter and iterate the array to add them, instead of concatenating them and adding them in one loop.

StringBuilder sb = new StringBuilder();

foreach (MySampleClass c in dictSampleClass)
{
    sb.Append(c.VAR1);
    sb.Append(c.VAR2);
    sb.Append(c.VAR3);
    sb.Append("|");
}

string[] results = sb.ToString().Split('|');

for (int i = 0; i < dictSampleClass.Count; i++)
{
    string s = results[i];
    MySampleClass c = dictSampleClass[i];
    PerformSomeTask(s,c.VAR4); 
}

I infer no benefits to using this code – most likely doesn’t even work!

UPDATE: in light of the fast performance of string creation from multiple strings, if PerformSomeTask is your bottleneck, try to break the iteration of the strings into multiple threads – it won’t improve the efficiency of the code but you’ll be able to utilise multiple cores.