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S M Abrar Jahin
S M Abrar Jahin

Reputation: 14578

C# Conversion from List<List<int>> to IList<IList<int>>

I have a C# function like this-

public IList<IList<int>> Subsets(int[] nums)
{
    List<List<int>> output = new List<List<int>>();
    if (nums.Length == 0)
    {
        return output;    //Problem in this line
        //return null;
    }
    ........
    ........
    return output.Concat(Subsets(nums.Skip(1).ToArray())).ToList();
}

What I am finding is-

Severity    Code    Description Project File    Line    Suppression State

Error   CS0266
Cannot implicitly convert type 'System.Collections.Generic.List<System.Collections.Generic.List<int>>' to 'System.Collections.Generic.IList<System.Collections.Generic.IList<int>>'.

An explicit conversion exists (are you missing a cast?) LeetCode    D:\LeetCode\Solution.cs 13  Active

Error

Can anyone please help?

Upvotes: 1

Views: 1126

Answers (4)

eocron
eocron

Reputation: 7526

Though, I agree with other answers to create appropriate interface, you can do this without creating new list like Gur Galler proposed with a little bit of hardcore hacking:

[StructLayout(LayoutKind.Explicit)]
public struct Union
{
    [FieldOffset(0)]
    public List<List<int>> a;
    [FieldOffset(0)]
    public IList<IList<int>> b;

    public static IList<IList<int>> Cast(List<List<int>> list)
    {
        var u = new Union();
        u.a = list;
        return u.b;
    }
}

class Program
{
    static void Main(string[] args)
    {
        var lists = new List<List<int>>() { new List<int>() { 1, 2, 3 } };
        IList<IList<int>> casted = Union.Cast(lists);
    }
}

Upvotes: 0

S M Abrar Jahin
S M Abrar Jahin

Reputation: 14578

Thanks to @NetMage for the great comment.

I have changed

return new List<List<int>>();

to

return new List<IList<int>>();

Which works great for me.

Upvotes: 0

Pedro Lima
Pedro Lima

Reputation: 1606

Change

List<List<int>> output = new List<List<int>>();

to

List<IList<int>> output = new List<IList<int>>();

You can cast the outer list to IList, since List implements IList, but you can't force the cast of the type argument of List, so it should be declared as IList since the beginning.

Upvotes: 3

Gur Galler
Gur Galler

Reputation: 920

Try this:

IList<IList<int>> list2 = list.Cast<IList<int>>().ToList();

You have to add using System.Linq; for that.

Upvotes: 2

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