Unlocking the Power of Generics

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Unlocking the Power of Generics

• Matt Goebel
• Crowe Chizek
• CNUG February 15, 2006

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Agenda

• Traditional Collections and Drawbacks
• Introduction to Generics
• Value of Generics
• Syntax and Samples

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Traditional Collections

• System.Collection namespace introduced in 1.0
  version of .NET Framework
• Useful container types
• Lists
• Dictionaries
• Hashtables
• CollectionBase

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Sample Class Definition

• class Book
• private int bookNumber 0
• public int BookNumber
• get return this.bookNumber
• set this. bookNumber value
• public Book( int _bookNumber )
• this.bookNumber _bookNumber

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Sample ArrayList Use

• ArrayList bookList new ArrayList()
• for( int i 0 i lt 20 i)
• bookList.Add( new Book(i) )
• IEnumerator listEnum bookList.GetEnumerator()
• while( listEnum.MoveNext() )
• Console.WriteLine(0,
• ((Book)(listEnum.Current)).BookNumber)

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Drawbacks

• No type checking enforcement at compile time
• Doesnt prevent adding unwanted types
• Can lead to difficult to troubleshoot issues
• Runtime errors!
• All items are stored as objects
• Must be cast going in and coming out
• Performance overhead of boxing and unboxing
  specific types

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Enforcing Consistent Types

• Can control and eliminate unwanted types
• Create wrapper class for each type

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Enforcing Consistent Types

• private class BookCollection CollectionBase
• public Book this int index
• get return (Book) Listindex
• set Listindex value
• public int Add( Book.BookNumber )
• return List.Add(BookNumber)
• public void Remove( Book.BookNumber )
• List.Remove( BookNumber )

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Enforcing Consistent Types

• BookCollection bookCol new BookCollection ()
• for( int i 0 i lt 20 i)
• bookCol.Add( new Book(i) )
• IEnumerator listEnum bookCol.GetEnumerator()
• while( listEnum.MoveNext() )
• Console.WriteLine(0,
• ((Book)(listEnum.Current)).BookNumber)

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Drawbacks

• Previous example demonstrated enforcing
  consistent type use with 1.x
• Code generators such as CodeSmith can generate
  wrappers for you
• Larger code base even if it is by a code
  generator
• Still has performance overhead of boxing and
  unboxing

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The Generic Solution

• Open constructed types
• Classes defined without a specific type
• Type is specified when instantiated
• System.Collections.Generic namespace
• List array dynamically sized as needed
• Linked list doubly linked list
• Queue first in, first out collection of objects
• Stack last in, first out collection of objects

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The Generic Solution Continued

• Provides type safety at compile time
• No loss of performance or code bloat
• The .NET CLR recognizes Generics
• Only one definition of a parameterized data
  structure, no matter how many types are used
• Affects Microsoft Intermediate Language (MSIL)

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VB.NET Generics Sample 1

• Dim testCol As New List(Of int32)()
• For i as int32 0 To 19
• testCol.Add(i)
• Next
• For each someInt As int32 in testCol
• Console.WriteLine(0, someInt)
• Next

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C Generics Sample 1

• ArrayListltintgt testCol new ArrayListltintgt()
• for (int i 0 i lt 20 i)
• testCol.Add(i)
• foreach (int someInt in testCol)
• Console.WriteLine(0, someInt)

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VB.NET Generics Sample 2

• Dim bookList As New List(Of Book)()
• For i as int32 0 To 19
• bookList.Add(New Book(i))
• Next
• For each book As Book in bookList
• Console.WriteLine(0, book.BookNumber)
• Next

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C Generics Sample 2

• ArrayListltBookgt bookList new ArrayListltBookgt()
• for (int i 0 i lt 20 i)
• bookList.Add( new Book(i) )
• foreach (Book book in bookList)
• Console.WriteLine(0, book.BookNumber)

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C Templates?

• Generics are NOT equal to Templates
• Compile-Time vs. Run-Time
• Templates Compile-Time
• Generics Run-Time
• Code Bloat?
• Pros and Cons for each

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Create Your Own Generics

• Generics can be applied a number of ways
• Classes
• Public Class MyType(Of T, U)
• public class MyTypeltT,Ugt
• Method return types and parameters
• Public Function Foo() As T
• public T Foo()
• Fields and properties
• Indexers, properties, events, structs,
  interfaces, etc.

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Example of Create Your Own Generic

• public class MyGenericltTgt
• private static int objectCount 0
• public MyGeneric()
• objectCount
• public int Count
• get return objectCount
• public T SomeMethod()

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Example of Create Your Own Generic

• Class SomeApplication
• static void Main(string args)
• MyGenericltintgt myIntGeneric new
  MyGenericltintgt()
• MyGenericltintgt myIntGeneric2 new
  MyGenericltintgt()
• int someInt myIntGeneric.SomeMethod()
• MyGenericltBookgt myBookGeneric new
  MyGenericltBookgt()
• Book someBook myBookGeneric.SomeMethod()
• Console.WriteLine(myIntGeneric.Count)
• Console.WriteLine(myIntGeneric2.Count)
• Console.WriteLine(myBookGeneric.Count)
• Console.WriteLine(new MyGenericltBookgt().Count)

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Generic Methods

• Can overload generic methods
• Method signatures can be a challenge
• Type parameters influence signature
• Return type does not influence signature
• Examples
• Public ListltIgt FooltI, Jgt(I val1, ListltJgt val2)
  
• Public void FooltK, Lgt(K val1, ListltLgt val2)

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Constraints

• Can apply constraints to limit the types used for
  the type parameter
• Public Class MyClass(Of T As IMyClassA,
  IMyClassB)
• End Class
• Public class MyClassltTgt where T IMyClassA,
  IMyClassB

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Default Values

• Assign a default value when the type is not known
  until implementation
• Assigns null for reference types
• Assigns appropriate default value for built-in
  types
• Only available in C for now
• public class MyClass ltK, Vgt
• public V Lookup(K key)
• V retVal default(V)
• return retVal

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Nullable Types

• Built-in data types such as int dont offer a
  good way to check if it has been assigned a value
• System.NullableltTgt offers a nullable type
• Nullableltintgt intVal null
• if (!intVal.HasValue)
• Console.WriteLine("Is null")
• intVal 0
• if (intVal.HasValue)
• Console.WriteLine("Has value")

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Power Collections

• Open source library of generics
  http//www.wintellect.com/powercollections
• Microsoft support and participation
• Additional useful types
• BigList
• Deque
• OrderedDictionary
• OrderedSet
• And more

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More Information

• An Introduction to C Generics
  -http//msdn.microsoft.com/library/default.asp?url
  /library/en-us/dnvs05/html/csharp_generics.asp
• Generics in .NET Type Safety, Performance and
  Generality -http//www.codeguru.com/columns/dotne
  t/article.php/c9661/
• Power Collections - http//www.wintellect.com/powe
  rcollections/
• Generics in .NET 2.0 - http//www.ondotnet.com/p
  ub/a/dotnet/2005/06/20/generics.html

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Need a Job?

• Were Hiring Full Time Employees that have .NET
  development skills
• Contact Tara Rodts
• trodts_at_crowechizek.com