Question

in .net, it is possible to write:

(from n in numbers where n == 5 select n).ToList();

without those brackets, it is not possible to call the ToList() method. how can i explain to someone what this line does (all i can say is it precompiles the query, but i do not know if this is actually 100% correct).

Answer 1

That looks to me like a LINQ expression wrapped in parentheses, the result of which will be IEnumerable<int> followed by a call to the IEnumerable<T> extension method ToList<T>().

I think in this case, the call ToList<T> forces the expression to be evaluated immediately, essentially foregoing any laziness to the evaluation.

Eric White wrote a good article on Lazy (and Eager) Evaluation with LINQ