Direct vs indirect enumerator call

Benchmark.cs

using System.Collections.Generic;
using BenchmarkDotNet.Attributes;

namespace Benchmarks
{
    public class EnumeratorBenchmarks
    {
        private const int SIZE = 1_000_000;

        private static readonly int[] array = GetArray();
        private static readonly IEnumerable<int> enumerable = GetArray();

        public static int[] GetArray()
        {
            var a = new int[SIZE];
            for (int i = 0; i < SIZE; i++)
            {
                a[i] = i;
            }

            return a;
        }

        [Benchmark]
        public int Array_sum()
        {
            var sum = 0;
            foreach (var i in array)
            {
                sum += i;
            }

            return sum;
        }

        [Benchmark]
        public int Enumerable_sum()
        {
            var sum = 0;
            foreach (var i in enumerable)
            {
                sum += i;
            }

            return sum;
        }
    }
}

Results.md

BenchmarkDotNet=v0.10.14, OS=Windows 10.0.17134
Intel Core i7-7700HQ CPU 2.80GHz (Kaby Lake), 1 CPU, 8 logical and 4 physical cores
.NET Core SDK=2.1.300-rc1-008673
  [Host]     : .NET Core 2.0.7 (CoreCLR 4.6.26328.01, CoreFX 4.6.26403.03), 64bit RyuJIT
  DefaultJob : .NET Core 2.0.7 (CoreCLR 4.6.26328.01, CoreFX 4.6.26403.03), 64bit RyuJIT

Method	Mean	Error	StdDev
Array_sum	632.2 us	15.60 us	23.82 us
Enumerable_sum	6,147.8 us	122.89 us	131.50 us