This document discusses boxing and unboxing in .NET. It begins by defining boxing as allocating an object to store a value type, while unboxing extracts the value type from the object. It then demonstrates through examples that boxing and unboxing have performance overhead compared to using value types directly. The document also discusses issues that can occur with boxing/unboxing like exceptions from incompatible type conversions. Finally, it recommends tools like ILDasm, ILspy and BoxCop for detecting boxing/unboxing in code.

1. BOXING & UNBOXING
Larry Nung

2. AGENDA
Boxing/UnBoxing
Issue for boxing/unboxing
How to find out boxing/Unboxing
2

3. BOXING/UNBOXING
3

4. BOXING
 Value Type => Object
 New object must be allocated and constructed
 Expensive computationally
4
int i = 123;
object o = i; // explicit boxing

5. UNBOXING
 Extracts value type from the object
 Expensive computationally
5
int i = 123; // a value type
object o = i; // boxing
int j = (int)o; // unboxing

6. ISSUE FOR BOXING/UNBOXING
6

7. ISSUE FOR BOXING/UNBOXING
7
using System;
using System.Diagnostics;
internal class Program {
private static void Main(string[] args) {
var count = 1000000000;
Console.WriteLine(“Boxing: {0} ms",
DoTest(count, () => {
var value = 123;
object value2 = value;
}));
Console.WriteLine(“None boxing: {0} ms",
DoTest(count, () => {
var value = 123;
var value2 = value;
}));
}
static long DoTest(int count, Action action) {
var sw = Stopwatch.StartNew();
for (int i = 0; i < count; ++i) action();
return sw.ElapsedMilliseconds;
}
}
0
2000
4000
6000
8000
10000
12000
1000000 10000000 100000000 1000000000
Boxing
None boxing

8. ISSUE FOR BOXING/UNBOXING
8
using System;
using System.Diagnostics;
internal class Program {
private static void Main(string[] args) {
var count = 1000000000;
Console.WriteLine("Boxing: {0} ms",
DoTest(count, () => {
var value = 123;
var value2 = string.Format("{0}", value);
}));
Console.WriteLine("None Boxing: {0} ms",
DoTest(count, () => {
var value = 123;
var value2 = string.Format("{0}", value.ToString());
}));
}
static long DoTest(int count, Action action) {
var sw = Stopwatch.StartNew();
for (int i = 0; i < count; ++i) action();
return sw.ElapsedMilliseconds;
}
}
0
50000
100000
150000
200000
250000
Boxing
None Boxing

9. ISSUE FOR BOXING/UNBOXING
9
using System;
internal class Program {
private static void Main(string[] args)
{
try {
var value1 = 1;
object value2 = value1;
var value3 = (float)value2;
} catch (Exception ex) {
Console.WriteLine(ex);
}
}
}

10. ISSUE FOR BOXING/UNBOXING
10
using System;
internal class Program
{
private static void Main(string[] args)
{
object a = 1;
object b = 1;
bool value = a == b;
bool value2 = a.Equals(b);
Console.WriteLine(value);
Console.WriteLine(value2);
}
}

11. ISSUE FOR BOXING/UNBOXING
11
using System;
internal class Program
{
private static void Main(string[] args)
{
object a = 1;
object b = 1;
bool value = a == b;
bool value2 = a.Equals(b);
Console.WriteLine(value);
Console.WriteLine(value2);
}
}

12. ISSUE FOR BOXING/UNBOXING
12
using System;
struct Counter
{
private int x;
public void Increment() { this.x++; }
public int Count { get { return this.x; } }
}
internal class Riddle
{
public readonly object counter = new Counter();
}
internal class Program
{
private static void Main(string[] args)
{
var riddle = new Riddle();
((Counter)riddle.counter).Increment();
Console.WriteLine(((Counter)riddle.counter).Count);
}
}

13. ISSUE FOR BOXING/UNBOXING
13
using System;
struct Counter
{
private int x;
public void Increment() { this.x++; }
public int Count { get { return this.x; } }
}
internal class Riddle
{
public readonly object counter = new Counter();
}
internal class Program
{
private static void Main(string[] args)
{
var riddle = new Riddle();
((Counter)riddle.counter).Increment();
Console.WriteLine(((Counter)riddle.counter).Count);
}
}

14. HOW TO FIND OUT
BOXING/UNBOXING
14

15. ILDASM
15

16. ILSPY
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17. .NET REFLECTOR
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18. BOXCOP
 For .NET 3.5
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19. RESHARPER - HEAP ALLOCATION VIEWER
EXTENSION
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20. RESHARPER - HEAP ALLOCATION VIEWER
EXTENSION
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21. RESHARPER - HEAP ALLOCATION VIEWER
EXTENSION
21

22. CLR C# HEAP ALLOCATION ANALYZER
 For Visual Studio 2015
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23. REFERENCE
 Boxing and Unboxing (C# Programming Guide)
 https://msdn.microsoft.com/en-
us//library/yz2be5wk.aspx?f=255&MSPPError=-
2147217396
 [C#]Effective C# 條款十七：盡量減少裝箱與拆箱 -
Level Up- 點部落
 http://www.dotblogs.com.tw/larrynung/archive/2011/03/0
8/21712.aspx
 [.NET Resource]透過BoxCop偵測程式是否存在
Boxing與UnBoxing - Level Up- 點部落
 http://www.dotblogs.com.tw/larrynung/archive/2013/03/0
1/94727.aspx 23

24.  ReSharper - Heap Allocation Viewer Extension -
Level Up
 http://larrynung.github.io/2014/08/12/resharper-heap-
allocation-viewer-extension/
 Clr C# Heap Allocation Analyzer - Level Up
 http://larrynung.github.io/2014/11/05/clr-c-number-heap-
allocation-analyzer/
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25. QUESTION & ANSWER
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