1. Visual C# 2005: Language Enhancements
12/4/2018 4:23 PM
Visual C# 2005: Language Enhancements
Luca Bolognese
C# Program Manager
Microsoft Corporation
© 2004 Microsoft Corporation. All rights reserved.
This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

2. C# Language Enhancements
12/4/2018 4:23 PM
C# Language Enhancements
Generics
Anonymous methods
Nullable types
Iterators
Partial types
and many more…
100% backwards compatible
© 2004 Microsoft Corporation. All rights reserved.
This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

3. Generics public class List { private object[] elements;
12/4/2018 4:23 PM
Generics
public class List {
private object[] elements;
private int count;
public void Add(object element) {
if (count == elements.Length) Resize(count * 2);
elements[count++] = element; }
public object this[int index] {
get { return elements[index]; }
set { elements[index] = value; }
public int Count {
get { return count; }
public class List<T> {
private T[] elements;
private int count;
public void Add(T element) {
if (count == elements.Length) Resize(count * 2);
elements[count++] = element; }
public T this[int index] {
get { return elements[index]; }
set { elements[index] = value; }
public int Count {
get { return count; }
List<int> intList = new List<int>();
intList.Add(1); // No boxing
intList.Add(2); // No boxing
intList.Add("Three"); // Compile-time error
int i = intList[0]; // No cast required
List intList = new List();
intList.Add(1);
intList.Add(2);
intList.Add("Three");
int i = (int)intList[0];
List intList = new List();
intList.Add(1); // Argument is boxed
intList.Add(2); // Argument is boxed
intList.Add("Three"); // Should be an error
int i = (int)intList[0]; // Cast required
© 2004 Microsoft Corporation. All rights reserved.
This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

4. Generics Why generics? How are C# generics implemented?
12/4/2018 4:23 PM
Generics
Why generics?
Type checking, no boxing, no downcasts
Reduced code bloat (typed collections)
How are C# generics implemented?
Instantiated at run-time, not compile-time
Checked at declaration, not instantiation
Work for both reference and value types
Complete run-time type information
© 2004 Microsoft Corporation. All rights reserved.
This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

5. Generics Type parameters can be applied to
12/4/2018 4:23 PM
Generics
Type parameters can be applied to
Class, struct, interface, delegate types
class Dictionary<K,V> {...}
struct HashBucket<K,V> {...}
interface IComparer<T> {...}
delegate R Function<A,R>(A arg);
Dictionary<string,Customer> customerLookupTable;
Dictionary<string,List<Order>> orderLookupTable;
Dictionary<string,int> wordCount;
© 2004 Microsoft Corporation. All rights reserved.
This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

6. Generics Type parameters can be applied to
12/4/2018 4:23 PM
Generics
Type parameters can be applied to
Class, struct, interface, delegate types
Methods
class Utils {
public static T[] CreateArray<T>(int size) {
return new T[size]; }
public static void SortArray<T>(T[] array) {
...
string[] names = Utils.CreateArray<string>(10);
names[0] = "Jones";
...
Utils.SortArray(names);
© 2004 Microsoft Corporation. All rights reserved.
This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

7. Generics Type parameters can be applied to
12/4/2018 4:23 PM
Generics
Type parameters can be applied to
Class, struct, interface, delegate types
Methods
Type parameters can have constraints
class Dictionary<K,V>: IDictionary<K,V>
where K: IComparable<K>
where V: IKeyProvider<K>, IPersistable, new()
{ public void Add(K key, V value) {
... }
class Dictionary<K,V> where K: IComparable {
public void Add(K key, V value) {
...
if (key.CompareTo(x) == 0) {...} }
class Dictionary<K,V> {
public void Add(K key, V value) {
...
if (((IComparable)key).CompareTo(x) == 0) {...} }
© 2004 Microsoft Corporation. All rights reserved.
This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

8. Generics Zero or one primary constraint
12/4/2018 4:23 PM
Generics
Zero or one primary constraint
Actual class, class, or struct
Zero or more secondary constraints
Interface or type parameter
Zero or one constructor constraint
new()
class Link<T> where T: class {...}
class Nullable<T> where T: struct {...}
class Relation<T,U> where T: class where U: T {...}
© 2004 Microsoft Corporation. All rights reserved.
This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

9. Generics Collection classes Collection interfaces
12/4/2018 4:23 PM
Generics
List<T>
Dictionary<K,V>
SortedDictionary<K,V>
Stack<T>
Queue<T>
Collection classes
Collection interfaces
Collection base classes
Utility classes
Reflection
IList<T>
IDictionary<K,V>
ICollection<T>
IEnumerable<T>
IEnumerator<T>
IComparable<T>
IComparer<T>
Collection<T>
KeyedCollection<T>
ReadOnlyCollection<T>
Nullable<T>
EventHandler<T>
Comparer<T>
© 2004 Microsoft Corporation. All rights reserved.
This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

10. Anonymous Methods class MyForm : Form { ListBox listBox;
12/4/2018 4:23 PM
Anonymous Methods
class MyForm : Form {
ListBox listBox;
TextBox textBox;
Button addButton;
public MyForm() {
listBox = new ListBox(...);
textBox = new TextBox(...);
addButton = new Button(...);
addButton.Click += delegate {
listBox.Items.Add(textBox.Text); }; }
class MyForm : Form {
ListBox listBox;
TextBox textBox;
Button addButton;
public MyForm() {
listBox = new ListBox(...);
textBox = new TextBox(...);
addButton = new Button(...);
addButton.Click += new EventHandler(AddClick); }
void AddClick(object sender, EventArgs e) {
listBox.Items.Add(textBox.Text);
© 2004 Microsoft Corporation. All rights reserved.
This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

11. Anonymous Methods Allows code block in place of delegate
12/4/2018 4:23 PM
Anonymous Methods
Allows code block in place of delegate
Delegate type automatically inferred
Code block can be parameterless
Or code block can have parameters
In either case, return types must match
button.Click += delegate { MessageBox.Show("Hello"); };
button.Click += delegate(object sender, EventArgs e) { MessageBox.Show(((Button)sender).Text); };
© 2004 Microsoft Corporation. All rights reserved.
This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

12. Anonymous Methods Method group conversions
12/4/2018 4:23 PM
Anonymous Methods
Method group conversions
Delegate type inferred when possible
using System;
using System.Threading;
class Program {
static void Work() {...}
static void Main() {
Thread t = new Thread(new ThreadStart(Work));
t.Start(); }
using System;
using System.Threading;
class Program {
static void Work() {...}
static void Main() {
Thread t = new Thread(Work);
t.Start(); }
© 2004 Microsoft Corporation. All rights reserved.
This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

13. Generics Performance 12/4/2018 4:23 PM
© 2004 Microsoft Corporation. All rights reserved.
This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

14. Nullable Types System.Nullable<T>
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Nullable Types
System.Nullable<T>
Provides nullability for any value type
Struct that combines a T and a bool
public struct Nullable<T> where T: struct {
public Nullable(T value) {...}
public T Value { get {...} }
public bool HasValue { get {...} }
... }
Nullable<int> x = new Nullable<int>(123);
...
if (x.HasValue) Console.WriteLine(x.Value);
© 2004 Microsoft Corporation. All rights reserved.
This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

15. Nullable Types T? same as System.Nullable<T>
12/4/2018 4:23 PM
Nullable Types
T? same as System.Nullable<T>
null literal conversions
Nullable conversions
int? x = 123;
double? y = 1.25;
int? x = null;
double? y = null;
int i = 123;
int? x = i; // int --> int? double? y = x; // int? --> double?
int? z = (int?)y; // double? --> int?
int j = (int)z; // int? --> int
© 2004 Microsoft Corporation. All rights reserved.
This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

16. Nullable Types Lifted conversions and operators Comparison operators
12/4/2018 4:23 PM
Nullable Types
Lifted conversions and operators
Comparison operators
Null coalescing operator
int? x = GetNullableInt();
int? y = GetNullableInt();
int? z = x + y;
int? x = GetNullableInt();
if (x == null) Console.WriteLine("x is null");
if (x < 0) Console.WriteLine("x less than zero");
int? x = GetNullableInt();
int i = x ?? 0;
© 2004 Microsoft Corporation. All rights reserved.
This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

17. Iterators foreach relies on “enumerator pattern”
12/4/2018 4:23 PM
Iterators
foreach relies on “enumerator pattern”
GetEnumerator() method
foreach makes enumerating easy
But enumerators are hard to write!
foreach (object obj in list) {
DoSomething(obj); }
Enumerator e = list.GetEnumerator();
while (e.MoveNext()) {
object obj = e.Current;
DoSomething(obj); }
© 2004 Microsoft Corporation. All rights reserved.
This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

18. Iterators public class ListEnumerator : IEnumerator { List list;
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Iterators
public class ListEnumerator : IEnumerator {
List list;
int index;
internal ListEnumerator(List list) {
this.list = list;
index = -1; }
public bool MoveNext() {
int i = index + 1;
if (i >= list.count) return false;
index = i;
return true;
public object Current {
get { return list.elements[index]; }
public class List {
internal object[] elements;
internal int count;
public IEnumerator GetEnumerator() { return new ListEnumerator(this); }
public class List {
internal object[] elements;
internal int count;
public IEnumerator GetEnumerator() { for (int i = 0; i < count; i++) {
yield return elements[i]; }
© 2004 Microsoft Corporation. All rights reserved.
This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

19. 12/4/2018 4:23 PM
Iterators
public IEnumerator GetEnumerator() {
return new __Enumerator(this); }
private class __Enumerator : IEnumerator {
object current;
int state;
public bool MoveNext() {
switch (state) {
case 0:
current = "Hello";
state = 1;
return true;
case 1:
current = "World";
state = 2;
return true; default:
return false;
public object Current {
get { return current; }
Method that incrementally computes and returns a sequence of values
yield return and yield break
Must return IEnumerator or IEnumerable
public class Test {
public IEnumerator GetEnumerator() {
yield return "Hello"; yield return "World"; }
© 2004 Microsoft Corporation. All rights reserved.
This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

20. Iterators public class List<T> {
12/4/2018 4:23 PM
Iterators
public class List<T> {
public IEnumerator<T> GetEnumerator() {
for (int i = 0; i < count; i++)
yield return elements[i]; }
public IEnumerable<T> Descending() {
for (int i = count - 1; i >= 0; i--)
public IEnumerable<T> Subrange(int index, int n) {
for (int i = 0; i < n; i++)
yield return elements[index + i];
List<Item> items = GetItemList();
foreach (Item x in items) {...}
foreach (Item x in items.Descending()) {...}
foreach (Item x in Items.Subrange(10, 20)) {...}
© 2004 Microsoft Corporation. All rights reserved.
This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

21. Partial Types public partial class Customer { private int id;
12/4/2018 4:23 PM
Partial Types
public partial class Customer {
private int id;
private string name;
private string address;
private List<Orders> orders; }
public class Customer {
private int id;
private string name;
private string address;
private List<Orders> orders;
public void SubmitOrder(Order order) {
orders.Add(order); }
public bool HasOutstandingOrders() {
return orders.Count > 0;
public partial class Customer {
public void SubmitOrder(Order order) {
orders.Add(order); }
public bool HasOutstandingOrders() {
return orders.Count > 0;
© 2004 Microsoft Corporation. All rights reserved.
This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

22. Static Classes Only static members
12/4/2018 4:23 PM
Static Classes
Only static members
Cannot be used as type of variable, parameter, field, property, …
Examples include System.Console, System.Environment
public static class Math {
public static double Sin(double x) {...}
public static double Cos(double x) {...}
... }
© 2004 Microsoft Corporation. All rights reserved.
This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

23. Property Accessors Different accessor accessibility
12/4/2018 4:23 PM
Property Accessors
Different accessor accessibility
One accessor can be restricted further
Typically set {…} more restricted
public class Customer {
private string id;
public string CustomerId {
get { return id; }
internal set { id = value; } }
© 2004 Microsoft Corporation. All rights reserved.
This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

24. 12/4/2018 4:23 PM
External Aliases
Enables use of identically named types in different assemblies
namespace Stuff {
public class Utils
public static void F() {...} }
foo.dll
extern alias Foo;
extern alias Bar;
class Program {
static void Main() {
Foo.Stuff.Utils.F();
Bar.Stuff.Utils.F(); }
namespace Stuff {
public class Utils
public static void F() {...} }
bar.dll
C:\>csc /r:Foo=foo.dll /r:Bar=bar.dll test.cs
© 2004 Microsoft Corporation. All rights reserved.
This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

25. Namespace Alias Qualifiers
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Namespace Alias Qualifiers
Enables more version resilient code
A::B looks up A only as alias
global::X looks up in global namespace
using IO = System.IO;
class Program {
static void Main() {
IO::Stream s = new IO::File.OpenRead("foo.txt");
global::System.Console.WriteLine("Hello"); }
© 2004 Microsoft Corporation. All rights reserved.
This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

26. Inline Warning Control
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Inline Warning Control
#pragma warning
using System;
class Program {
[Obsolete]
static void Foo() {}
static void Main() {
#pragma warning disable 612
Foo();
#pragma warning restore 612 }
© 2004 Microsoft Corporation. All rights reserved.
This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

27. Fixed Size Buffers C style arrays in unsafe code
12/4/2018 4:23 PM
Fixed Size Buffers
C style arrays in unsafe code
public struct OFSTRUCT {
public byte cBytes;
public byte fFixedDisk;
public short nErrCode;
private int Reserved;
public fixed char szPathName[128]; }
© 2004 Microsoft Corporation. All rights reserved.
This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

28. Want to know more? http://msdn.microsoft.com/vcsharp/language
12/4/2018 4:23 PM
Want to know more?
© 2004 Microsoft Corporation. All rights reserved.
This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

29. © 2004 Microsoft Corporation. All rights reserved.
12/4/2018 4:23 PM
© 2004 Microsoft Corporation. All rights reserved.
This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.
© 2004 Microsoft Corporation. All rights reserved.
This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.