Initialize list from array using a initializer list

Question

A base class have readonly field of type List<SomeEnum> which the derived classes will initialize. Now, there is a derived class in which I want to add the all the values of the SomeEnum. One way is to type all the enum values, but the enum is a little big, so is there any other way to do it?

public class Base
{
 private readonly List<SomeEnum> _list;

 protected Base(List<SomeEnum> list)
 {
  _list = list;
 }
}

public class Derived : Base
{
 public Derived() : base(new List<SomeEnum>() { Enum.GetValues(typeof(SomeEnum)) }
 {
 }
}

(The above code would not compile, I believe intializers don't accept arrays.)

You may want to accept IEnumerable<SomeEnum> or IList<SomeEnum> in the base constructor for future flexibility. — Merlyn Morgan-Graham
– Merlyn Morgan-Graham, Commented Jan 7, 2011 at 7:34

user47589 · Accepted Answer · 2011-01-07 07:39:35Z

4

It's because you have to cast the result of Enum.GetValues to the appropriate IEnumerable<T> type. See here:

using System.Linq;


public class Derived : Base
{
    public Derived()
        : base(new List<SomeEnum>(Enum.GetValues(typeof(SomeEnum)).OfType<SomeEnum>()))
    {
    }
}

answered Jan 7, 2011 at 7:39

user47589

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1 Comment

user47589 Over a year ago

You have to import System.Linq.

vc 74 · Accepted Answer · 2011-01-07 07:31:48Z

2

As Mark wrote, there is a List constructor that accepts an enumerable, maybe you can leverage it the following (less coupled) way:

public class Base 
{     
  private readonly List<UserActions> _list;      

  protected Base(IEnumerable<UserActions> values)
  {         _list = new List<UserActions>(values);  
  } 
}  

public class Derived : Base 
{     
   public Derived() : base((UserActions[]) Enum.GetValues(typeof(UserActions))
  { 
  }
}

answered Jan 7, 2011 at 7:31

vc 74

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Comments

Mark Byers · Accepted Answer · 2011-01-07 09:12:44Z

2

That won't work because the collection initializer calls Add with your argument, and you can't add an Array to a List using the Add method (you'd need AddRange instead).

However there is a constructor for List<T> can accept IEnumerable<T>. Try this:

new List<SomeEnum>((IEnumerable<SomeEnum>)Enum.GetValues(typeof(SomeEnum)))

edited Jan 7, 2011 at 9:12

answered Jan 7, 2011 at 7:27

Mark Byers

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2 Comments

user47589 Over a year ago

This does not compile. Enum.GetValues returns an Array, which does not implement IEnumerable<T>. It is not a generic.

user47589 Over a year ago

I don't know why this answer is being voted up. It doesn't work. See my answer for one that does work.

David Conde · Accepted Answer · 2011-01-07 07:28:10Z

1

Did you tried passing the array of values in the constructor of the list, like this:

public Derived() : 
         base(new List<SomeEnum>(Enum.GetValues(typeof(UserActions))) 
{}

answered Jan 7, 2011 at 7:28

David Conde

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2 Comments

akif Over a year ago

Arrays do not implement IEnumerable. So the code doesn't compiles.

Mark Byers Over a year ago

@hab: Actually arrays do implement IEnumerable.

akif · Accepted Answer · 2011-01-07 07:51:41Z

1

base(new List<SomeEnum>(((IEnumerable<SomeEnum>)Enum.GetValues(typeof(SomeEnum)).GetEnumerator())))

I got it working by casting the enumerator returned to the generic type (which List accepts.)

answered Jan 7, 2011 at 7:51

akif

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