Casting vs Converting an object toString, when object really is a string

Question

This isn't really an issue, however I am curious. When I save a string in lets say an DataRow, it is cast to Object. When I want to use it, I have to cast it ToString. As far as I know there are several ways of doing this, first is

string name = (string)DataRowObject["name"]; //valid since I know it's a string 

and another one is:

string name = DataRowObject["name"].ToString(); 

I am interested in what is the difference between both? Is the first more efficient? (This is just a speculation, in my head ToString() method is implemented by some looping mechanism where just casting it "could" be faster, however this is just a "gut feeling" I have).

Is there even a faster / more elegant way of doing this?

Can anyone clear this up for me?

Answer 1

The two are intended for different purposes. The ToString method of any object is supposed to return a string representation of that object. Casting is quite different, and the 'as' key word performs a conditional cast, as has been said. The 'as' key word basically says "get me a reference of this type to that object if that object is this type" while ToString says "get me a string representation of that object". The result may be the same in some cases but the two should never be considered interchangeable because, as I said, they exist for different purposes. If your intention is to cast then you should always use a cast, NOT ToString.

from http://www.codeguru.com/forum/showthread.php?t=443873

see also http://bytes.com/groups/net-c/225365-tostring-string-cast

Answer 2

If you know it is a String then by all means cast it to a String. Casting your object is going to be faster than calling a virtual method.

Edit: Here are the results of some benchmarking:

============ Casting vs. virtual method ============ cast 29.884 1.00 tos  33.734 1.13 

I used Jon Skeet's BenchmarkHelper like this:

using System; using BenchmarkHelper;  class Program {     static void Main()     {         Object input = "Foo";         String output = "Foo";          var results             = TestSuite.Create("Casting vs. virtual method", input, output)             .Add(cast)             .Add(tos)             .RunTests()             .ScaleByBest(ScalingMode.VaryDuration);          results.Display(ResultColumns.NameAndDuration | ResultColumns.Score,                 results.FindBest());     }      static String cast(Object o)     {         return (String)o;     }      static String tos(Object o)     {         return o.ToString();     } } 

So it appears that casting is in fact slightly faster than calling ToString().