private static void Main(string[] args)
{
    string test = "   Hello, World! ";
    Console.WriteLine(Trim(test.ToCharArray()).ToArray());
}

private static Span<char> Trim(Span<char> source)
{
    if (source.IsEmpty)
    {
        return source;
    }

    int start = 0, end = source.Length - 1;
    char startChar = source[start], endChar = source[end];

    while ((start < end) && (startChar == ' ' || endChar == ' '))
    {
        if (startChar == ' ')
        {
            start++;
        }

        if (endChar == ' ')
        {
            end—;
        }

        startChar = source[start];
        endChar = source[end];
    }

    return source.Slice(start, end - start + 1);
}