Writing a Better Comparison<T> for complex Ts

[jehugaleahsa@gmail.com]

Hello:

I find myself writing Comparison<Tdel egates that looks like this:

private static int compareCustomer s(Customer lhs, Customer rhs)
{
int result = Comparer<string >.Default.Compa re(lhs.LastName ,
rhs.LastName);
if (result == 0)
{
result = Comparer<string >.Default.Compa re(lhs.FirstNam e,
rhs.FirstName);
}
return result;
}

Is this pretty standard?

This approach is fine up to the point where you have to compare more
than two or three fields.

Does anyone have a more elegant method for writing complex
Comparison<T>'s ?

Thanks,
Travis

[Jon Skeet [C# MVP]]

Re: Writing a Better Comparison&lt;T &gt; for complex Ts

jehugaleahsa@gm ail.com <jehugaleahsa@g mail.comwrote:

I find myself writing Comparison<Tdel egates that looks like this:
>
private static int compareCustomer s(Customer lhs, Customer rhs)
{
int result = Comparer<string >.Default.Compa re(lhs.LastName ,
rhs.LastName);
if (result == 0)
{
result = Comparer<string >.Default.Compa re(lhs.FirstNam e,
rhs.FirstName);
}
return result;
}
>
Is this pretty standard?
>
This approach is fine up to the point where you have to compare more
than two or three fields.
>
Does anyone have a more elegant method for writing complex
Comparison<T>'s ?

In MiscUtil (http://pobox.com/~skeet/csharp/miscutil) we have a
ProjectionCompa rer and an extension method, so you can say:

IComparer<Custo mercomparer =
ProjectionCompa rer.Create(cust =cust.LastName)
.ThenBy(Project ionComparer.Cre ate(cust =cust.FirstName ));
etc

This could probably be beefed up even further with a bit of effort, to
be honest.

--
Jon Skeet - <skeet@pobox.co m>
Web site: http://www.pobox.com/~skeet
Blog: http://www.msmvps.com/jon_skeet
C# in Depth: http://csharpindepth.com

[jehugaleahsa@gmail.com]

Re: Writing a Better Comparison&lt;T &gt; for complex Ts

In MiscUtil (http://pobox.com/~skeet/csharp/miscutil) we have a

ProjectionCompa rer and an extension method, so you can say:
>
IComparer<Custo mercomparer =
    ProjectionCompa rer.Create(cust =cust.LastName)
       .ThenBy(Project ionComparer.Cre ate(cust =cust.FirstName ));
etc
>
This could probably be beefed up even further with a bit of effort, to
be honest.
>
--
Jon Skeet - <sk...@pobox.co m>
Web site:http://www.pobox.com/~skeet 
Blog:http://www.msmvps.com/jon_skeet
C# in Depth:http://csharpindepth.com- Hide quoted text -
>
- Show quoted text -

Stuck back in my 2.0 world, I have written this before:

private delegate int lameComparison( );

private static int customerCompare r(Customer lhs, Customer rhs)
{
lameComparison[] comparisons = {
delegate() { return
Comparer<string >.Default.Compa re(lhs.LastName , rhs.LastName); },
delegate() { return
Comparer<string >.Default.Compa re(lhs.FirstNam e, rhs.FirstName); },
};
int result = 0;
for (int i = 0; i != comparisons.Len gth && result == 0; ++i)
{
result = comparisons[i]();
}
return result;
}

However, this not only makes my coworkers froth at the mouth, it has
performance hits (minimal).

One more reason to move to 3.0.

Thanks,
Travis