为什么.Concat方法的返回值类型看起来有点奇怪：System.Linq.Enumerable +（...）？

Question

I have 2 instances:

  foo and bar 

Their types are:

 foo.GetType().ToString()

returns: System.Collections.Generic.List`1[MyNameSpace.MyClass]

bar.GetType().ToString()

returns: System.Collections.Generic.List`1[MyNameSpace.MyClass]

When I concatanate them:

var foobar = foo.Concat(bar);

The GetType() returns System.Linq.Enumerable+d__71`1[MyNameSpace.MyClass]

Question : What does this mean? Should not it be IEnumerable ?

Answer 1

Don't confuse the declared return type and the actual type of the returned value. Concat is declared to return IEnumerable<T> , but it actually returns an instance of a concrete type that implements IEnumerable<T> . GetType returns the concrete type, not the declared return type.

As for the weird name, Concat is implemented with an iterator block , and iterator blocks are transformed by the compiler into types with names such as Enumerable+d__71 that implement IEnumerable<T> .

Answer 2

In addition to Thomas' answer, note that the "`1" portion of the name indicates the number of generic arguments. The type for each generic argument follows in the brackets "[...]".