Is the string ctor the fastest way to convert an IEnumerable to string

Question

Edited for the release of .Net Core 2.1

Repeating the test for the release of .Net Core 2.1, I get results like this

1000000 iter

Answer 1

It's worth noting that these results, whilst true for the case of IEnumerable from a purists point of view, are not always thus. For example if you were to actually have a char array even if you are passed it as an IEnumerable it is faster to call the string constructor.

The results:

Sending String as IEnumerable 
10000 iterations of "new string" took 157ms. 
10000 iterations of "sb inline" took 150ms. 
10000 iterations of "string.Concat" took 237ms.
======================================== 
Sending char[] as IEnumerable 
10000 iterations of "new string" took 10ms.
10000 iterations of "sb inline" took 168ms.
10000 iterations of "string.Concat" took 273ms.

The Code:

static void Main(string[] args)
{
    TestCreation(10000, 1000);
    Console.ReadLine();
}

private static void TestCreation(int iterations, int length)
{
    char[] chars = GetChars(length).ToArray();
    string str = new string(chars);
    Console.WriteLine("Sending String as IEnumerable");
    TestCreateMethod(str, iterations);
    Console.WriteLine("===========================================================");
    Console.WriteLine("Sending char[] as IEnumerable");
    TestCreateMethod(chars, iterations);
    Console.ReadKey();
}

private static void TestCreateMethod(IEnumerable testData, int iterations)
{
    TestFunc(chars => new string(chars.ToArray()), testData, iterations, "new string");
    TestFunc(chars =>
    {
        var sb = new StringBuilder();
        foreach (var c in chars)
        {
            sb.Append(c);
        }
        return sb.ToString();
    }, testData, iterations, "sb inline");
    TestFunc(string.Concat, testData, iterations, "string.Concat");
}