.drc

If you use Func only, you’re restricted to being able to test against only objects that are already in memory, which is inefficient when large numbers of objects are involved.

I took a shot at exactly that here: http://ubik.com.au/article/named/implementing_the_specification_pattern_with_linq – hopefully the article might shed some light on how specs using Linq can be used for the dual purposes of in-memory and database object selection.

Cheers!
Nick

1. There’s no need to take an Expression[Func[T,bool]] type, as this just means more work at runtime to compile it – instead you can just take a Func[T,bool] which will be compiled at compile-time.

2. You don’t need to write _expression.Invoke(obj) – you can simply write _expression(obj) because it is a method in itself.

Also – you allow null in the constructor so should probably check for this in the IsSatisfiedBy method, because at the moment you could pass null to the constructor then get a NullReferenceException in that method.