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CSharp · Console

/Program.cs

using System;
using System.Collections.Generic;

namespace testread
{
    internal static class Program
    {
        static void Main(string[] args)
        {
            var input1 = new[] { 1, 2 };
            Foo(input1);

            var input2 = new List<int> { 3, 4, 5 };
            Foo(input2);
        }

        private static void Foo(IReadOnlyCollection<int> bar)
        {
            Console.WriteLine(bar.Count);
        }
    }
}