In C#, out keyword 是argument传值变成passed by reference. out keyword 在同时返回多个值时很有用.

与ref keyword 相似. 若是使用out keyword传argument, 那么在method 的definition 和 使用时都需要家out keyword. 

Async methods can't use out keyword.

 

Differences between out keyword and ref keyword:

ref requires that variable be initialized before it is passed.

1 class OutReturnExample 2 { 3     static void Method(out int i, out string s1, out string s2) 4     { 5         i = 44; 6         s1 = "I've been returned"; 7         s2 = null; 8     } 9     static void Main()10     {11         int value;12         string str1, str2;13         Method(out value, out str1, out str2);14         // value is now 4415         // str1 is now "I've been returned"16         // str2 is (still) null;17     }18 }