System.Collections.Generic.List requires '1' type arguments

I have this error whith the following code:

string[] colors = { "green", "brown", "blue", "red" };
var list = new List(colors);
IEnumerable query = list.Where(c => c.length == 3);
list.Remove("red");
Console.WriteLine(query.Count());

Moreover, Count() does not seem to be allowed anymore. Is it deprecated?

4 Answers

You are trying to create a List<string> and you should tell that to the compiler

var list = new List<string>(colors);

There is no List, there is a generic class named List<T>, requires a type parameter.You can't create a generic list without specifying the type parameter.

Also you are trying to call Count extension method.That method takes IEnumerable<T> as first parameter,not IEnumerable, here is the definition:

public static int Count<TSource>(this IEnumerable<TSource> source)

so you should use IEnumerable<string> to access that extension method:

IEnumerable<string> query = list.Where(c => c.Length == 3);
list.Remove("red");
Console.WriteLine(query.Count());

You are using System.Collections.Generic.List<T>, so it is a generic list, therefore you must provide the generic parameter T. In your example case, you want a List<string>. So try:

List<string> list = new List<string>(colors);

Actually, you don't need a List at all in your sample and you can simplify everything a lot:

var count = new [] { "green", "brown", "blue", "red" } .Where(c => c.length == 3) .Where(c => c != "red") .Count();
Console.WriteLine(count);

Try this:

static void Main(string[] args)
{ string[] colors = { "green", "brown", "blue", "red" }; var list = new List<string>(colors); // <string> IEnumerable query = list.Where(c => c.Length == 3); // "Length", not "length" list.Remove("red"); Console.WriteLine(query.Count());
}