将查询理解翻译为LINQ中的Enumerable扩展方法

Question

How do I translate the following query to functional calls? I know the compiler does this behind the scenes but don't know how I would view the result

        var query = from item in Enumerable.Range(0, 10)
                    from item2 in Enumerable.Range(item, 10)
                    from item3 in Enumerable.Range(item2, 10)
                    select new { item, item2, item3 };

Answer 1

In this case, it uses SelectMany , and a concept called transparent identifiers which preserve the existing range variables. So your query would translate to:

var query = Enumerable.Range(0, 10)
                      .SelectMany(item => Enumerable.Range(item, 10),
                                  (item, item2) => new { item, item2 })
                      .SelectMany(z => Enumerable.Range(z.item2, 10),
                                  (z, item3) => new { z.item, z.item2, item3 });

(In this case z is the transparent identifier. If there'd been a where clause or anything other than a select after the last from clause, another transparent identifier would have been introduced.)

The translations are all described in the C# language specification, section 7.16.