generic List<T> Sort()

shadowcodes · February 13th, 2007, 03:51 AM

hi,

im new to csharp and im learning it through the professional c# 2005 book..im little confused with the below code

Code:

public class RacerComparer : IComparer<Racer>
{
public enum CompareType
{
Name,
Car
}

private CompareType compareType;
public RacerComparer(CompareType compareType)
{
this.compareType = compareType;
}

public int Compare(Racer x, Racer y)
{
int result = 0;
switch (compareType)
{
case CompareType.Name:
result = x.Name.CompareTo(y.Name);
break;
case CompareType.Car:
result = x.Car.CompareTo(y.Car);
break;
}
return result;
}
}

Code:

racers.Sort(new RacerComparer(RacerComparer.CompareType.Car));

and here the comparer method takes 2 parameters of type Racer ..but in the implementation we never pass 2 parameters to this method..and if this sort method is sorting the list<T> why do we provide 2 parameters of that type please help me

philip_cole · February 14th, 2007, 04:28 PM

Hi,

Sorting and comparing is often a little confusing to begin with, but if you think about what the Sort method is actually doing it can help.

When you call racers.Sort, the list will think, OK I've got all these Racer objects, and I've got to somehow put them in the right order. Luckily I got passed this RacerComparer object to help me...

Because RacerComparer implements IComparer<Racer>, the list knows that if it passes any TWO Racer objects to RacerComparer.Compare(), it will get told which one should come first. So it goes through all the possible pairs of Racers it contains and passes them to the Compare method. Depending on what gets returned, it will add them into the appropriate place in the list.

In terms of the list<T> part, remember T get replaced with whatever Type of object we are dealing with. If we tried using a RacerComparer with a List<int>, it would be sending numbers to the Compare method, which obviously doesn't make sense. By using IComparer<Racer> the compiler knows we are using the correct sort of object.

Hopefully this hasn't confused you even more!

Phil

shadowcodes · February 15th, 2007, 01:30 PM

thanks alot..now im really cleared with that:)..hats off to you..

no more confusions:D