using System;

using System.Collections.Generic;

using System.Runtime.InteropServices;               

using System.Diagnostics;

​

public class User : IFreeable {

    public string Name {get;set;}

    public int Age {get;set;}

    public string Email {get;set;}

    public bool Freed {get;set;}

    public void Reset() {

        Name = null;

        Age = 0;

        Email = null;

        Freed = true;

    }

}

​

public class Program

{

    public static void Main()

    {

        var allocator = new Allocator<User>(5);

        var user = allocator.Alloc();

        user.Name = "Ben1";

        user.Age = 35;

        user.Email = "ben1@buildstarted.com";

​

        var user2 = allocator.Alloc();

        user2.Name = "Ben2";

        user2.Age = 35;

        user2.Email = "ben2@buildstarted.com";  

​

        var user3 = allocator.Alloc();

        user3.Name = "Ben3";

        user3.Age = 35;

        user3.Email = "ben3@buildstarted.com";  

​

        var user4 = allocator.Alloc();

        user4.Name = "Ben4";

        user4.Age = 35;

        user4.Email = "ben4@buildstarted.com";  

​

        var user5 = allocator.Alloc();

        user5.Name = "Ben5";

        user5.Age = 35;

        user5.Email = "ben5@buildstarted.com";  

        try { 

            var user6 = allocator.Alloc();

        } catch (Exception) {

            Console.WriteLine("Unable to allocate 6 users");

        }

        allocator.Free(user);

        var user7 = allocator.Alloc();

        user7.Name = "Ben7";

    }

}

​

public interface IFreeable {

    bool Freed {get;set;}

    void Reset();

}

​

public class Allocator<T> where T: IFreeable, new() {

    private T[] _managed;

    private int _freeEnd;

    public Allocator(int capacity, bool preallocate)

    {

        _managed = new T[capacity];

        if (preallocate)

        {

            for (int i = 0; i != capacity; ++i)

            {

                _managed[i] = new T();

                _managed[i].Reset();

            }

            _freeEnd = capacity;

        }

    }

    public T Alloc()

    {

        T result = default(T);

        if (_freeEnd == 0)

        {

            result = new T();

        }

        else

        {

            result = _managed[--_freeEnd];

        }

        result.Reset();

        return result;

    }

    public void Free(T obj)

    {

        Debug.Assert(!obj.Freed);

        if (_freeEnd < _managed.Length)

        {

            _managed[_freeEnd++] = obj;

            obj.Freed = true;

        }

        else

        {

            throw new Exception("Can't store more than " + _managed.Length + " free objects");

        }

    }

}

​