Converting Array to IEnumerable<T>

问题

To my surprise, I get the following statement:

public static IEnumerable<SomeType> AllEnums 
  => Enum.GetValues(typeof(SomeType));

to complain about not being able to convert from System.Array to System.Collection.Generic.IEnumerable. I thought that the latter was inheriting from the former. Apparently I was mistaken.

Since I can't LINQ it or .ToList it, I'm not sure how to deal with it properly. I'd prefer avoiding explicit casting and, since it's a bunch of values for an enum, I don't think as SomeType-ing it will be of much use, neither.

回答1:

The general Array base class is not typed, so it does not implement any type-specific interfaces; however, a vector can be cast directly - and GetValues actually returns a vector; so:

public static IEnumerable<SomeType> AllEnums
    = (SomeType[])Enum.GetValues(typeof(SomeType));

or perhaps simpler:

public static SomeType[] AllEnums 
    = (SomeType[])Enum.GetValues(typeof(SomeType));

回答2:

I thought that the latter was inheriting from the former.

Enum.GetValues returns Array, which implements the non-generic IEnumerable, so you need to add a cast:

public static IEnumerable<SomeType> AllEnums = Enum.GetValues(typeof(SomeType))
    .Cast<SomeType>()
    .ToList(); 

This works with LINQ because Cast<T> extension method is defined for the non-generic IEnumerable interface, not only on IEnumerable<U>.

Edit: A call of ToList() avoid inefficiency associated with walking multiple times an IEnumerable<T> produced by LINQ methods with deferred execution. Thanks, Marc, for a great comment!

来源：https://stackoverflow.com/questions/27744199/converting-array-to-ienumerablet