1. Visual C# "Whidbey": Language Enhancements
11/22/2018 1:47 AM
Session Code: TLS320
Visual C# "Whidbey": Language Enhancements
Anders Hejlsberg
Distinguished Engineer
Microsoft Corporation
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This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

2. C# Language Enhancements
11/22/2018 1:47 AM
C# Language Enhancements
Generics
Anonymous methods
Iterators
Partial types
Other enhancements
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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;
11/22/2018 1:47 AM
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
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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?
11/22/2018 1:47 AM
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
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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
Class, struct, interface, and 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;
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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
Class, struct, interface, and delegate types
Methods
string[] names = Utils.CreateArray<string>(3);
names[0] = "Jones";
names[1] = "Anderson";
names[2] = "Williams";
Utils.SortArray(names);
class Utils {
public static T[] CreateArray<T>(int size) {
return new T[size]; }
public static void SortArray<T>(T[] array) { …
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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
Class, struct, interface, and delegate types
Methods
Type parameters can have constraints
One base class, multiple interfaces, new()
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) {…} }
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This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

8. Generics Generics are “invariant”
11/22/2018 1:47 AM
Generics
Generics are “invariant”
Interfaces can be used for type neutrality
public class List<T>: IList {
public void Add(T item) {…}
public T this[int index] {…} … }
public class List<T> {
public void Add(T item) {…}
public T this[int index] {…} … }
public interface IList {
public void Add(object item);
public object this[int index] {…} … }
object
List<object>
List<int>
List<string>
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This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

9. Generics T.default Null checks Type casts void Foo<T>() {
11/22/2018 1:47 AM
Generics
void Foo<T>() {
T x = null; // Error
T y = T.default; // Ok }
T.default
Null checks
Type casts
void Foo<T>(T x) {
if (x == null) {
throw new FooException(); } …
void Foo<T>(T x) {
int i = (int)x; // Error
int j = (int)(object)x; // Ok }
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This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

10. Generics Collection classes Collection interfaces
11/22/2018 1:47 AM
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>
© Microsoft Corporation. All rights reserved.
This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

11. Generics System.Nullable<T> Provides nullability for any type
11/22/2018 1:47 AM
Generics
System.Nullable<T>
Provides nullability for any type
Struct that combines a T and a bool
Conversions between T and Nullable<T>
Conversion from null literal to Nullable<T>
Nullable<int> x = 123;
Nullable<int> y = null;
int i = (int)x;
int j = x.Value;
if (x.HasValue) Console.WriteLine(x.Value);
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This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

12. Anonymous Methods class MyForm : Form { ListBox listBox;
11/22/2018 1:47 AM
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);
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This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

13. Anonymous Methods Allows code block in place of delegate
11/22/2018 1:47 AM
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); };
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This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

14. Anonymous Methods Code block can access local variables
11/22/2018 1:47 AM
Anonymous Methods
Code block can access local variables
public class Bank {
List<Account> GetLargeAccounts(double minBalance) {
Helper helper = new Helper();
helper.minBalance = minBalance;
return accounts.FindAll(helper.Matches); }
internal class Helper
internal double minBalance;
internal bool Matches(Account a) {
return a.Balance >= minBalance;
} }
public class Bank {
List<Account> accounts;
List<Account> GetOverdrawnAccounts() {
return accounts.FindAll(delegate(Account a) {
return a.Balance < 0;
}); }
List<Account> GetLargeAccounts(double minBalance) {
return a.Balance >= minBalance;
delegate bool Predicate<T>(T item);
public class List<T> {
public List<T> FindAll(Predicate<T> filter) {
List<T> result = new List<T>();
foreach (T item in this) {
if (filter(item)) result.Add(item); }
return result;
© Microsoft Corporation. All rights reserved.
This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

15. Anonymous Methods Method group conversions
11/22/2018 1:47 AM
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(); }
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This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

16. Generics Performance 11/22/2018 1:47 AM
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This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

17. Iterators foreach relies on “enumerator pattern”
11/22/2018 1:47 AM
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); }
© 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;
11/22/2018 1:47 AM
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 ListEnumerator GetEnumerator() { return new ListEnumerator(this); }
© Microsoft Corporation. All rights reserved.
This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

19. 11/22/2018 1:47 AM
Iterators
public IEnumerator GetEnumerator() {
return new __Enumerator(this); }
private class __Enumerator: IEnumerator {
object current;
int state;
public bool MoveNext() {
switch (state) {
case 0: …
case 1: …
case 2: … …
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 List {
public IEnumerator GetEnumerator() {
for (int i = 0; i < count; i++) { yield return elements[i]; }
© 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> {
11/22/2018 1:47 AM
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--) yield return elements[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)) {…}
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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;
11/22/2018 1:47 AM
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;
© Microsoft Corporation. All rights reserved.
This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

22. 11/22/2018 1:47 AM
Partial Types
© Microsoft Corporation. All rights reserved.
This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

23. Other Enhancements Static classes Can contain only static members
11/22/2018 1:47 AM
Other Enhancements
Static classes
Can contain only static members
Cannot be type of variable, parameter, etc.
System.Console, System.Environment, etc.
public static class Math {
public static double Sin(double x) {…}
public static double Cos(double x) {…} … }
© Microsoft Corporation. All rights reserved.
This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

24. Other Enhancements Property accessor accessibility
11/22/2018 1:47 AM
Other Enhancements
Property accessor accessibility
Allows one accessor to be restricted further
Typically set {…} more restricted than get {…}
public class Customer {
private string id;
public string CustomerId {
get { return id; }
internal set { id = value; } }
© Microsoft Corporation. All rights reserved.
This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

25. Other Enhancements Namespace alias qualifier
A::B looks up A only as namespace alias
global::X starts lookup 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"); }
© Microsoft Corporation. All rights reserved.
This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

26. Other Enhancements Fixed size buffers
11/22/2018 1:47 AM
Other Enhancements
Fixed size buffers
C style embedded arrays in unsafe code
public struct OFSTRUCT {
public byte cBytes;
public byte fFixedDisk;
public short nErrCode;
private int Reserved;
public fixed char szPathName[128]; }
© Microsoft Corporation. All rights reserved.
This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

27. Other Enhancements #pragma warning
11/22/2018 1:47 AM
Other Enhancements
#pragma warning
Control individual warnings in blocks of code
using System;
class Program {
[Obsolete]
static void Foo() {}
static void Main() {
#pragma warning disable 612
Foo();
#pragma warning restore 612 }
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This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

28. C# and CLI Standardization
11/22/2018 1:47 AM
C# and CLI Standardization
Work begun in September 2000
Intel, HP, IBM, Fujitsu, Plum Hall, and others
ECMA standards ratified December 2001
ISO standards published April 2003
Several CLI and C# implementations
.NET Framework and Visual Studio .NET
“SSCLI” – Shared source on XP, FreeBSD, OS X
“Mono” – Open source on Linux
Standardization of new features ongoing
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This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

29. Book signing, Exhibition Hall Book Store, Wednesday, 1-2pm
11/22/2018 1:47 AM
Book signing, Exhibition Hall Book Store, Wednesday, 1-2pm
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This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

30. Q & A C# Language home page ECMA C# Standard
11/22/2018 1:47 AM
Q & A
C# Language home page
ECMA C# Standard
publications/standards/ecma-334.htm
Panel: The Future of .NET Languages
PNL10, Thursday, 1:45pm – 3:15pm
Tools Lounge (near Hall A)
Tuesday, 5:15pm – 6:30pm
Wednesday, 3:00pm – 5:00pm
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This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

31. © 2003-2004 Microsoft Corporation. All rights reserved.
11/22/2018 1:47 AM
© Microsoft Corporation. All rights reserved.
This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.
© Microsoft Corporation. All rights reserved.
This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

32. 11/22/2018 1:47 AM
© Microsoft Corporation. All rights reserved.
This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.