using System;

using System.Collections.Generic;

using System.Linq;

​

public class Program

{

    public static void Main()

    {

        var foos = new List<Foo>()

        {

            new Foo(true, 1),

            new Foo(false, 2)

        };

        // works

        var actives = foos.Where(x => x.IsActive=true).ToList();

        // returns 2!

        Console.WriteLine(actives.Count);

        // compile error

        var ages = foos.Where(x => x.Age = 1).ToList();

    }

}

​

public class Foo {

    public Foo(bool active, int age)

    {

        this.IsActive = active;

        this.Age = age;

    }

​

    public bool IsActive { get; set; }

    public int Age { get; set; }

}