获取不同的结果（IEqualityComparer比较器）

Question

As a LINQ-beginner I wonder why nobody mentioned in Implementing IEqualityComparer<T> for comparing arbitrary properties of any class (including anonymous) that the query actually has to be carried out to get the results. In other words, just calling
IEnumerable<Person> people = ... ; // some database call here var distinctPeople = people.Distinct(new PropertyComparer<Person>("FirstName"));
will not trigger the execution of the specific Equals(Tx, Ty) and GetHashCode(T obj) methods in the PropertyComparer.

The message "Expanding the Results View will enumerate the IEnumerable" (in the Debugger) gave me the hint. Now, could I proceed with something like foreach (var dp in distinctPeople) to get the results?

Answer 1

This has nothing at all to do with the IEqualityComparer . It is entirely based on the method you're providing it to, in this case, Distinct . Distinct , along with all of the LINQ methods that return an IEnumerable , defer execution as much as possible, only performing the work that they need to compute the results when they actually need to do so.