Implement SingleOrNew

[atifaziz]

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

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Originally reported on Google Code with ID 12

Reported by @jskeet on 2009-02-18 16:19:03

[atifaziz]

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();
}

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Reported by @atifaziz on 2009-02-18 17:04:12

[atifaziz]

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...

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Reported by @cammerman on 2009-02-19 15:54:24

[atifaziz]

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.

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Reported by @jskeet on 2009-02-20 09:38:53

[atifaziz]

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

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Reported by @jskeet on 2009-02-20 10:28:40

[atifaziz]

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 :)

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Reported by tormod.steinsholt on 2012-06-16 12:05:36

[fsateler]

This is already implemented as SingleOrFallback, but a FirstOrFallback is missing

[fsateler]

I think that SingleOrFallback should not exist, and instead provide FallbackIfEmpty, the same way that SingleOrDefault does not provide a way to specify the default value.

[atifaziz]

@fsateler Agree and this has been dormant for almost 7 years anyway! Closing this as addition of FallbackIfEmpty is now being followed-up in #122.