Boxing/UnBoxing Continued

Since my last post I ran across some new questions.
1. Does boxing have a performance issue or UnBoxing?
2. In case when an int has to be concatenated with string is it better to use ToString() method.

After running some tests I have concluded.
Boxing is slower than UnBoxing and ToString() is slower than boxing. So if one cannot avoid boxing do not try to use ToString() methods they seem to be slower.

My current challenge is that I have a Winform screen with 15 drop downs and 6 grids. In order to bind the the controls I am converting strongly typed Business entities to DataTables. There are quite a few properties in the business entities which are int and DateTime resulting in boxing and impacting the performance of the screens.

Hopefully I will come up with a solution to this issue soon.

Boxing/Unboxing

Its been nearly three years since I last blogged and what better topic to start blogging back again than boxing/unboxing.

Most of the literature that I can find online tells me what is a boxing/unboxing operation or what are its disadvantages but none could definitively answer to the question that came up during a recent code review. Whether this code causes boxing/unboxing

class Class1

{

int i = 10;

static void Main(string[] args)

{

Class1 x = new Class1();

int a = x.i; //unboxing??

x.i= 20; //boxing??

}

}

I myself when initially came across the concept of boxing/unboxing used to think that the above code will cause box and unbox operations to be called but that's not the case. The above code does not cause boxing/unboxing.

The idea of boxing unboxing is a little little difficult to grasp and I have found lots of people(including myself) struggling with it. There is an article on type fundamentals by Jeffrey Richter which may help explain things and also there is a blog post by David Cumps which gives a nice visual explanation of boxing/unboxing

To figure out in the C# code if it has any box operation look for the following

1. An instance of a value type is assigned to a variable/field/property of the type object
2. An instance of a value type is cast to an instance of an object type
3. An instance of a value type is passed to a method/property indexer which has object type as a parameter.

To figure out in C# code if it has any Unbox operation check whether an instance of a type object is being cast to an instance of a value type.

Below are the few common cases of boxing and unboxing

int j;

int i = 10; // can be any value type like float, double, Point, DateTime, structures etc.

//The standard example

object o = i; //implicit boxing

o = (object)i; //explicit boxing

j = (int)o; //unboxing

//String.Format and its variations

string.Format("Boxing {0}",i); //implicit boxing

Console.WriteLine("Boxing {0}",i);

StringBuilder strBuild = new StringBuilder();

strBuild.AppendFormat("Boxing {0}",i); //implicit boxing

//Collections

ArrayList list = new ArrayList();

list.Add(i); //implicit boxing

list.BinarySearch(i); //implicit boxing

list.IndexOf(i); //implicit boxing

list.Insert(2,i); //implicit boxing (only for i)

list.LastIndexOf(i); //implicit boxing

list.Remove(i); //implicit boxing

j = (int) list[0]; //unboxing

Hashtable coll = new Hashtable();

coll.Add(i,i); //implicit boxing(twice)

coll.Contains(i); //implicit boxing

coll.ContainsKey(i); //implicit boxing

coll.ContainsValue(i); //implicit boxing

coll.Remove(i); //implicit boxing

j = (int) coll[i]; //implicit boxing for indexer and unboxing for assignment

//DataTable

DataTable dt = new DataTable();

dt.Columns.Add("UntypedColumn");

dt.Columns.Add("IntColumn",typeof(int));

DataRow dr = dt.NewRow();

dr["UntypedColumn"] = i; //implicit boxing

dr["IntColumn"] = i; //implicit boxing

j = (int) dr["UntypedColumn"]; //unboxing

j = (int) dr["UntypedColumn"]; //unboxing