Implement SingleOrNew

[GoogleCodeExporter]

Implement SingleOrNew as per 
http://stackoverflow.com/questions/561762/what-about-a-singleornew-method-
instead-of-singleordefault-in-linq/561787#561787

Original issue reported on code.google.com by jonathan.skeet on 18 Feb 2009 at 4:19

[GoogleCodeExporter]

If we overload DefaultIfEmpty to take a delegate (as you propose for
SingleOrSpecifiedDefault) then Single and other similar operators can be 
composed on
top as usual. For example:

var client = db.Clients
    .Where(c => c.Name == "Some Client")
    .DefaultIfEmpty(() => new Client())
    .Single();

SingleOrNew (if still needed as a helper) can then be implemented in terms of
DefaultIfEmpty plus Single.

public static T SingleOrNew<T>(this IEnumerable<T> source) 
    where T : new()
{
    return source.DefaultIfEmpty(() => new T()).Single();
}

Original comment by azizatif on 18 Feb 2009 at 5:04

[GoogleCodeExporter]

I like the idea of an override for DefaultIfEmpty to take a delegate.  I think 
that
if we then also override SingleOrDefault to take a similar delegate, that would 
cover
the problem space we're looking at without making completely new methods...

Original comment by CAmmerman@gmail.com on 19 Feb 2009 at 3:54

[GoogleCodeExporter]

I'm not sure about overloading SingleOrDefault - too easy to confuse people, 
IMO. I 
like SingleOrFallback which was suggested elsewhere though. Likewise we can do 
FallbackIfEmpty.

Original comment by jonathan.skeet on 20 Feb 2009 at 9:38

[GoogleCodeExporter]

Implemented SingleOrFallback, but need an overload taking a predicate (just 
like 
SingleOrDefault). Will do FallbackIfEmpty too.

Original comment by jonathan.skeet on 20 Feb 2009 at 10:28

[GoogleCodeExporter]

I realize that it will be confusing, but it would be cool (in a fluent way) to 
just call it 
SingleOr<T>(IEnumerable<T>,Func<T>)  
as well as a FirstOr()

I'm not really suggesting it :)

Original comment by tormod.s...@gmail.com on 16 Jun 2012 at 12:05