Add more derived interfaces to Linq

[zms9110750]

After sorting, you will get the IOrderdEnumerable，
He has a special method called 'ThenBy' for subsequent sorting.
Because such subsequent sorting may have any number of times,
So we have this interface and method,
And it cannot be completed through method overloading.

But I think creating more unique interfaces and methods would be better.
For example, the GroupBy method can select the internal elements after the grouping is completed.

• If there is no parameter name, it is difficult to understand the delegation function solely based on the parameter position
• The ToLookup method has a similar effect but does not have such overloading.
• What if I want to SelectMany instead of Select for internal elements?

[huoyaoyuan]

IOrderdEnumerable exists solely because OrderBy().ThenBy() is a very common special sequence in SQL and data processing.

CreateOrderedEnumerable method is meant to be used exclusively by LINQ optimizer.

There won't by other unique interface, because LINQ uses its internal types for optimization, which is not a stable API. The usage of IOrderdEnumerable is to prevent you to write ThenBy() without OrderBy(), and warns for OrderBy().OrderBy().