https://msdn.microsoft.com/en-us/library/dn961160.aspx
int apples = 4; // Before C# 6.0 System.Console.WriteLine(String.Format("I have {0} apples", apples)); // C# 6.0 System.Console.WriteLine($"I have {apples} apples");
var result = string.Format("{0}{1}{2}{3}", tempChannelId, tempIndex, tempType, tempDeviceId);
升级为
var result = $"{tempChannelId}{tempIndex}{tempType}{tempDeviceId}";
优越性在于，不需要考虑{0}{1}{2}{3}和后面的变量的顺序对应
原文：http://www.cnblogs.com/chucklu/p/4970992.html