using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

        IEnumerable<Person> results;

        var people = new List<Person>(){

            new Person{ Name="Peter ",   Gender = Gender.Male},

            new Person{ Name="John  ",   Gender = Gender.Male},         

            new Person{ Name="Kevin ",   Gender = Gender.Male},             

            new Person{ Name="Julia ",   Gender = Gender.Female},           

            new Person{ Name="Sonya ",   Gender = Gender.Female},

            new Person{ Name="Rachel",   Gender = Gender.Female},

        };

        bool isGenderMaleChecked = true;    

        //1-method - bad, not wrong

        if(isGenderMaleChecked)

            results = people.Where(p => p.Gender.Equals(Gender.Male));

        else

            results = people.Where(p => !p.Gender.Equals(Gender.Male));

        //2-method - not so good, but better than first (ternary)

            results = people.Where(p => isGenderMaleChecked ? p.Gender.Equals(Gender.Male) : !p.Gender.Equals(Gender.Male));

        //3-method - good, but not so readable

            results = people.Where(p=> !isGenderMaleChecked ^ p.Gender.Equals(Gender.Male));

        //4-method - THE BEST, efficient and readable  

            results = people.Where(p=> isGenderMaleChecked == p.Gender.Equals(Gender.Male));

        foreach(var p in results)

        {

            Console.WriteLine(string.Format("Name: {0} || Gender: {1}",p.Name, p.Gender));                      

            Console.WriteLine("================================");

        }

    }

    public class Person{

        public string Name;

        public Gender Gender;

    }

    public enum Gender{

        Male, 

        Female,

        XiMale  

    }

}