如何在C＃中将IEnumerable <Enum>转换为Enum？

Question

I've parsed several strings into Enum flags but can't see a neat way of merging them into a single Enum bitfield.

The method I'm using loops through the string values then |= the casted values to the Enum object, like so:

[Flags]
public enum MyEnum { None = 0, First = 1, Second = 2, Third = 4 }
...

string[] flags = { "First", "Third" };
MyEnum e = MyEnum.None;

foreach (string flag in flags)
    e |= (MyEnum)Enum.Parse(typeof(MyEnum), flag, true);

I've tried using a Select method to convert to my Enum type, but then I'm stuck with IEnumerable<MyEnum> . Any suggestions?

Answer 1

Well, from an IEnumerable<MyEnum> you can use:

MyEnum result = parsed.Aggregate((current, next) => current | next);

or in order to accommodate an empty sequence:

MyEnum result = parsed.Aggregate(MyEnum.None, (current, next) => current | next);

It's basically the same thing as you've already got, admittedly...

So overall, the code would be:

MyEnum result = flags.Select(x => (MyEnum) Enum.Parse(typeof(MyEnum), x))
                     .Aggregate(MyEnum.None, (current, next) => current | next);

(You can perform it in a single Aggregate call as per Guffa's answer, but personally I think I'd keep the two separate, for clarity. It's a personal preference though.)

Note that my Unconstrained Melody project makes enum handling somewhat more pleasant, and you can also use the generic Enum.TryParse method in .NET 4.

So for example, using Unconstrained Melody you could use:

MyEnum result = flags.Select(x => Enums.ParseName<MyEnum>(x))
                     .Aggregate(MyEnum.None, (current, next) => current | next);

Answer 2

You can use the Aggregate method to put the flags together:

MyEnum e = flags
  .Select(s => (MyEnum)Enum.Parse(typeof(MyEnum), s, true))
  .Aggregate(MyEnum.None, (f, n) => f | n);