Why is var Int32 not List<Int32> in this example

Question

Ok I was in the process of getting an answer for another SO question, and I came up with the following function to get a distinct list of int's:

    static List<Int32> Example(params List<Int32> lsts)
    {
        List<Int32> result = new List<int>();

        foreach (var lst in lsts)
        {
            result = result.Concat(lst).ToList();
        }

        return result.Distinct().OrderBy(c => c).ToList();
    }

When I look at var in VS2012, it says its of type Int32 not List<Int32> . Shown here:

Shouldn't var be type List<Int32> ??

Answer 1

you are missing a [] at the end of the parameter type declaration:

//                                            v-- this is missing in your code
static List<Int32> Example(params List<Int32>[] lsts)
{
    List<Int32> result = new List<int>();

    foreach (var lst in lsts)
    {
        result = result.Concat(lst).ToList();
    }

    return result.Distinct().OrderBy(c => c).ToList();
}

Answer 2

You're being misled by a different compiler error.
Your parameter is not an array.

You need to change the parameter to params List<Int32>[] lsts to make it an array of lists. (or, better yet, params IEnumerable<Int32>[] lsts )

Note that you can also get rid of the foreach loop completely and write

return lsts.SelectMany(list => list)
           .Distinct()
           .OrderBy(i => i)
           .ToList();

Answer 3

带有关键字params必须是一个数组。