lambda-allocations.cs

using System;
using System.Collections.Generic;

class Program
{
    private static readonly Dictionary<int, Func<int, int>> _funcs = new Dictionary<int, Func<int, int>>();

    static void Main(string[] args)
    {
        for (int iter = 0; iter < 1000000; iter++)
        {
            for (int i = 1; i < 5; i++)
            {
                Func<int, int> func = GetFunc(i);
            }
        }
    }
    static Func<int, int> GetFunc(int i)
    {
        if (!_funcs.TryGetValue(i, out var ret))
        {
            // This causes no allocations
            ret = CreateFunc(i);

            // This causes mass allocations
            // ret = val => i + 1;

            _funcs.Add(i, ret);
        }
        return ret;
    }
    static Func<int, int> CreateFunc(int i)
    {
        return val => i + 1;
    }
}