Comments on: Functional Collection Parameters: Handling the null collection

By: Functional Collection Parameters: A different way of thinking about collections at Mark Needham

Fri, 19 Jun 2009 13:29:08 +0000

[...] written previously about the ways I’ve been making use of functional collection parameters in my code but what I hadn’t really considered was that the way of thinking [...]

By: Iain B

Iain B — Wed, 17 Jun 2009 10:04:09 +0000

I can’t remember if you’ve written about the null-coalescing operator ‘??’, but I’ve been using it a lot to remove all those annoying ‘if (x == null)’s

return (source ?? new List() ).Select(selector) ;

By: Mark Needham

Mark Needham — Tue, 16 Jun 2009 21:33:17 +0000

That’s a pretty neat idea, hadn’t thought of that. I guess that also has the benefit of making it more obvious what’s going on

By: Chris Ammerman

Chris Ammerman — Tue, 16 Jun 2009 15:48:18 +0000

Arg, all my generics got dropped by the sanitizer….

I also forgot to note that the EmptyIfNull approach is really nice because then all of the non-aggregatory IEnumerable operations will automatically work because they all know how to handle an empty collection! So, just one function to enable all operations, instead of one for each.

By: Chris Ammerman

Chris Ammerman — Tue, 16 Jun 2009 15:45:45 +0000

Another way around this is an extension method to IEnumerable that will pass through non-null source and return Enumerable.Empty() for a null source:

IEnumerable EmptyIfNull(this IEnumerable source)
{
if (source == null)
return Enumerable.Empty();

return source;
}

Then your function can look like this:

private IEnumerable MapFooMessages(IEnumerable fooMessages)
{
return
fooMessages
.EmptyIfNull()
.Select(eachFooMessage => new Foo(fooMessage));
}