using System;
using System.Linq.Expressions;
 
public static class Aaa
{
    public class A
    {
        public string NameField;
    }

public static void Copy(string sourceDirName, string destDirName, bool excludeSubdirectories)
{
    // Style #1: fluent
    Guard.MethodArgument("sourceDirName").IsNotNullOrEmpty(sourceDirName);
    Guard.MethodArgument("destDirName").IsNotNullOrEmpty(destDirName, "The destination directory is required!");
 
    // Style #2: lambdas and expressions
    Guard.Argument.IsNotNullOrWhiteSpace(()=>sourceDirName);
    Guard.Argument.IsNotNullOrWhiteSpace(()=>destDirName, "The destination directory is required!");

// usage:
// var constructor = GetConstructor<Foo>();
// IFoo foo = constructor();
 
 
private static Func<T> GetConstructor<T>() where T : class, new()
{
    ConstructorInfo constructorInfo = typeof(T).GetConstructor(new Type[0]);
    return Expression.Lambda<Func<T>>(Expression.New(constructorInfo))
                .Compile();

var _Offspring = _Context.Users   
        .SelectMany(x => x.Offspring).Distinct();

[TestMethod]
public void CanGetValueItemfromCollection()
{
    var col = new Collection<string> {"Hello", "World"};
    var testItem = col.GetValueItem(c => c.Equals("World"));
    Assert.AreEqual(testItem, "World");
}
 
[TestMethod]
public void CanGetReferenceItemfromCollectionByProperty()

/// <summary>
/// Find an object in a value-type collection.
/// </summary>
/// <typeparam name="T">Type of collection.</typeparam>
/// <param name="collection">The collection to search.</param>
/// <param name="isMatch">The Predicate to test to find the collection item.</param>
/// <returns>The collection item.</returns>
public static T GetValueItem<T>(this ICollection<T> collection, Predicate<T> isMatch)
{
    foreach (var item in collection)