using System;

using static System.Console;

using System.Linq;

using System.Collections.Generic;

using System.Diagnostics;

​

public class Program {

    public static void Main() {

        Executa(CriarCompras1);

        Executa(CriarCompras2);

        Executa(CriarCompras3);

        Executa(CriarCompras4);

        Executa(CriarCompras5);

        Executa(CriarCompras6);

    }

    public static void Teste() => WriteLine("Fazendo algo aqui");

    private static void Executa(Func<int, List<Compra>> metodo) {

        var stopwatch = new Stopwatch();

        stopwatch.Start();

        for (var i = 0; i < 1000; i++) metodo(50);

        stopwatch.Stop();

        WriteLine($"Tempo passado: {stopwatch.ElapsedTicks}");

    }

    private static List<Compra> CriarCompras1(int numComprasParaGerar) => new List<Compra>(Enumerable.Range(0, numComprasParaGerar).Select(i => new Compra()));

    private static List<Compra> CriarCompras2(int numComprasParaGerar) => new int[numComprasParaGerar].Select(i => new Compra()).ToList();

​

    private static List<Compra> CriarCompras3(int numComprasParaGerar) => (from i in new int[numComprasParaGerar] select new Compra()).ToList();

​

    private static List<Compra> CriarCompras4(int numComprasParaGerar) => new List<Compra>(Enumerable.Range(0, numComprasParaGerar).Select(i => new Compra()));

​

    private static List<Compra> CriarCompras5(int numComprasParaGerar) {

        var lstCompras = new List<Compra>();

        CriarCompras(lstCompras, numComprasParaGerar);

        return lstCompras;

    }

    private static void CriarCompras(List<Compra> lstCompras, int numComprasParaGerar) {

       lstCompras.Add(new Compra());

       if(lstCompras.Count < numComprasParaGerar) CriarCompras(lstCompras, numComprasParaGerar);

    }

​

    private static List<Compra> CriarCompras6(int numComprasParaGerar)  {

        List<Compra> lstCompras = new List<Compra>(numComprasParaGerar);

        for (int i = 0; i < numComprasParaGerar; i++) lstCompras.Add(new Compra());

        return lstCompras;

    }

}

​

public class Compra {

    public int Item = 0;

}