StringBuilder String string.Concat 字符串拼接速度

首先看测试代码：

public class StringSpeedTest
    {
        private readonly static string _testStr = "0123456789";

        public string StringAdd(int count)
        {
            string str = string.Empty;
            for (int i = 0; i < count; i++)
            {
                str += _testStr;
            }
            return str;
        }

        public string UseStringBuilder(int count)
        {
            StringBuilder sb = new StringBuilder();

            for (int i = 0; i < count; i++)
            {
                sb.Append(_testStr);
            }

            return sb.ToString();
        }
        public string UseStringBuilderWithCapacity(int count)
        {
            StringBuilder sb = new StringBuilder(count * _testStr.Length);

            for (int i = 0; i < count; i++)
            {
                sb.Append(_testStr);
            }

            return sb.ToString();
        }
        public string UseStringConcat(int count)
        {
            string[] list = new string[count];
            for (int i = 0; i < count; i++)
            {
                list[i] = _testStr;
            }
            return string.Concat(list);
        }
        public string UseStringConcatWithList(int count)
        {
            List<string> list = new List<string>(count);
            for (int i = 0; i < count; i++)
            {
                list.Add(_testStr);
            }
            return string.Concat(list);
        }
        public string UseStringConcatWithListToArray(int count)
        {
            List<string> list = new List<string>(count);
            for (int i = 0; i < count; i++)
            {
                list.Add(_testStr);
            }
            return string.Concat(list.ToArray());
        }
    }

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