Introduction to c#

Introduction to C#

Anders Hejlsberg
Distinguished Engineer
Developer Division
Microsoft Corporation

C# – The Big Ideas
The first component oriented
language in the C/C++ family
Everything really is an object
Next generation robust and
durable software
Preservation of investment

A component oriented language

C# is the first “component oriented”
language in the C/C++ family
Component concepts are first class:
Properties, methods, events
Design-time and run-time attributes
Integrated documentation using XML
Enables one-stop programming
No header files, IDL, etc.
Can be embedded in web pages

Everything really is an object

Traditional views
C++, Java: Primitive types are “magic” and do
not interoperate with objects
Smalltalk, Lisp: Primitive types are objects, but
at great performance cost
C# unifies with no performance cost
Deep simplicity throughout system
Improved extensibility and reusability
New primitive types: Decimal, SQL…
Collections, etc., work for all types

Robust and durable software

Garbage collection
No memory leaks and stray pointers
Exceptions
Error handling is not an afterthought
Type-safety
No uninitialized variables, unsafe casts
Versioning
Pervasive versioning considerations in
all aspects of language design

Preservation of Investment
C++ heritage
Namespaces, enums, unsigned types, pointers
(in unsafe code), etc.
No unnecessary sacrifices
Interoperability
What software is increasingly about
MS C# implementation talks to XML, SOAP,
COM, DLLs, and any .NET language
Millions of lines of C# code in .NET
Short learning curve
Increased productivity

Hello World
using System;

class Hello
{
static void Main() {
Console.WriteLine("Hello world");
}
}

C# Program Structure
Namespaces
Contain types and other namespaces
Type declarations
Classes, structs, interfaces, enums,
and delegates
Members
Constants, fields, methods, properties, indexers,
events, operators, constructors, destructors
Organization
No header files, code written “in-line”
No declaration order dependence

C# Program Structure
using System;

namespace System.Collections
{
public class Stack
{
Entry top;

public void Push(object data) {
top = new Entry(top, data);
}

public object Pop() {
if (top == null) throw new InvalidOperationException();
object result = top.data;
top = top.next;
return result;
}
}
}

Type System
Value types
Directly contain data
Cannot be null
Reference types
Contain references to objects
May be null
int i = 123;
string s = "Hello world";

i 123

s "Hello world"

Type System
Value types
Primitives int i;
Enums enum State { Off, On }
Structs struct Point { int x, y; }
Reference types
Classes class Foo: Bar, IFoo {...}
Interfaces interface IFoo: IBar {...}
Arrays string[] a = new string[10];

Delegates delegate void Empty();

Predefined Types
C# predefined types
Reference object, string
Signed sbyte, short, int, long
Unsigned byte, ushort, uint, ulong
Character char
Floating-point float, double, decimal
Logical bool
Predefined types are simply aliases
for system-provided types
For example, int == System.Int32

Classes
Single inheritance
Multiple interface implementation
Class members
Constants, fields, methods, properties,
indexers, events, operators,
constructors, destructors
Static and instance members
Nested types
Member access
public, protected, internal, private

Structs
Like classes, except
Stored in-line, not heap allocated
Assignment copies data, not reference
No inheritance
Ideal for light weight objects
Complex, point, rectangle, color
int, float, double, etc., are all structs
Benefits
No heap allocation, less GC pressure
More efficient use of memory

Classes And Structs
class CPoint { int x, y; ... }
struct SPoint { int x, y; ... }

CPoint cp = new CPoint(10, 20);
SPoint sp = new SPoint(10, 20);

10
sp
20

cp CPoint
10
20

Interfaces
Multiple inheritance
Can contain methods, properties,
indexers, and events
Private interface implementations
interface IDataBound
{
void Bind(IDataBinder binder);
}

class EditBox: Control, IDataBound
{
void IDataBound.Bind(IDataBinder binder) {...}
}

Enums
Strongly typed
No implicit conversions to/from int
Operators: +, -, ++, --, &, |, ^, ~
Can specify underlying type
Byte, short, int, long
enum Color: byte
{
Red = 1,
Green = 2,
Blue = 4,
Black = 0,
White = Red | Green | Blue,
}

Delegates
Object oriented function pointers
Multiple receivers
Each delegate has an invocation list
Thread-safe + and - operations
Foundation for events
delegate void MouseEvent(int x, int y);

delegate double Func(double x);

Func func = new Func(Math.Sin);
double x = func(1.0);

Unified Type System
Everything is an object
All types ultimately inherit from object
Any piece of data can be stored,
transported, and manipulated with no
extra work

object

Stream Hashtable int double

MemoryStream FileStream

Unified Type System
Boxing
Allocates box, copies value into it
Unboxing
Checks type of box, copies value out
int i = 123;
object o = i;
int j = (int)o;
i 123

o System.Int32
123
j 123

Unified Type System
Benefits
Eliminates “wrapper classes”
Collection classes work with all types
Replaces OLE Automation's Variant
Lots of examples in .NET Framework
string s = string.Format(
"Your total was {0} on {1}", total, date);

Hashtable t = new Hashtable();
t.Add(0, "zero");
t.Add(1, "one");
t.Add(2, "two");

Component Development
What defines a component?
Properties, methods, events
Integrated help and documentation
Design-time information
C# has first class support
Not naming patterns, adapters, etc.
Not external files
Components are easy to build
and consume

Properties
Properties are “smart fields”
Natural syntax, accessors, inlining

public class Button: Control
{
private string caption;

public string Caption {
get {
return caption;
}
set {
caption = value;
Repaint(); Button b = new Button();
} b.Caption = "OK";
} String s = b.Caption;
}

Indexers
Indexers are “smart arrays”
Can be overloaded

public class ListBox: Control
{
private string[] items;

public string this[int index] {
get {
return items[index];
}
set {
items[index] = value;
Repaint(); ListBox listBox = new ListBox();
} listBox[0] = "hello";
} Console.WriteLine(listBox[0]);
}

Events
Sourcing

Define the event signature
public delegate void EventHandler(object sender, EventArgs e);

Define the event and firing logic
public class Button
{
public event EventHandler Click;

protected void OnClick(EventArgs e) {
if (Click != null) Click(this, e);
}
}

Events
Handling

Define and register event handler
public class MyForm: Form
{
Button okButton;

public MyForm() {
okButton = new Button(...);
okButton.Caption = "OK";
okButton.Click += new EventHandler(OkButtonClick);
}

void OkButtonClick(object sender, EventArgs e) {
ShowMessage("You pressed the OK button");
}
}

Attributes
How do you associate information
with types and members?
Documentation URL for a class
Transaction context for a method
XML persistence mapping
Traditional solutions
Add keywords or pragmas to language
Use external files, e.g., .IDL, .DEF
C# solution: Attributes

Attributes
public class OrderProcessor
{
[WebMethod]
public void SubmitOrder(PurchaseOrder order) {...}
}

[XmlRoot("Order", Namespace="urn:acme.b2b-schema.v1")]
public class PurchaseOrder
{
[XmlElement("shipTo")] public Address ShipTo;
[XmlElement("billTo")] public Address BillTo;
[XmlElement("comment")] public string Comment;
[XmlElement("items")] public Item[] Items;
[XmlAttribute("date")] public DateTime OrderDate;
}

public class Address {...}

public class Item {...}

Attributes
Attributes can be
Attached to types and members
Examined at run-time using reflection
Completely extensible
Simply a class that inherits from
System.Attribute
Type-safe
Arguments checked at compile-time
Extensive use in .NET Framework
XML, Web Services, security, serialization,
component model, COM and P/Invoke interop,
code configuration…

XML Comments
class XmlElement
{
/// <summary>
/// Returns the attribute with the given name and
/// namespace</summary>
/// <param name="name">
/// The name of the attribute</param>
/// <param name="ns">
/// The namespace of the attribute, or null if
/// the attribute has no namespace</param>
/// <return>
/// The attribute value, or null if the attribute
/// does not exist</return>
/// <seealso cref="GetAttr(string)"/>
///
public string GetAttr(string name, string ns) {
...
}
}

Statements And
Expressions
High C++ fidelity
If, while, do require bool condition
goto can’t jump into blocks
Switch statement
No fall-through, “goto case” or “goto default”
foreach statement
Checked and unchecked statements
Expression statements must do work
void Foo() {
i == 1; // error
}

foreach Statement
Iteration of arrays
public static void Main(string[] args) {
foreach (string s in args) Console.WriteLine(s);
}

Iteration of user-defined collections
foreach (Customer c in customers.OrderBy("name")) {
if (c.Orders.Count != 0) {
...
}
}

Parameter Arrays
Can write “printf” style methods
Type-safe, unlike C++
void printf(string fmt, params object[] args) {
foreach (object x in args) {
...
}
}

printf("%s %i %i", str, int1, int2);

object[] args = new object[3];
args[0] = str;
args[1] = int1;
Args[2] = int2;
printf("%s %i %i", args);

Operator Overloading
First class user-defined data types
Used in base class library
Decimal, DateTime, TimeSpan
Used in UI library
Unit, Point, Rectangle
Used in SQL integration
SQLString, SQLInt16, SQLInt32,
SQLInt64, SQLBool, SQLMoney,
SQLNumeric, SQLFloat…

Operator Overloading
public struct DBInt
{
public static readonly DBInt Null = new DBInt();

private int value;
private bool defined;

public bool IsNull { get { return !defined; } }

public static DBInt operator +(DBInt x, DBInt y) {...}

public static implicit operator DBInt(int x) {...}
public static explicit operator int(DBInt x) {...}
}
DBInt x = 123;
DBInt y = DBInt.Null;
DBInt z = x + y;

Versioning
Problem in most languages
C++ and Java produce fragile base classes
Users unable to express versioning intent
C# allows intent to be expressed
Methods are not virtual by default
C# keywords “virtual”, “override” and “new”
provide context
C# can't guarantee versioning
Can enable (e.g., explicit override)
Can encourage (e.g., smart defaults)

Versioning
class Base // version 2
1
{
} public virtual void Foo() {
Console.WriteLine("Base.Foo");
}
}

class Derived: Base // version 1
2b
2a
{
new public virtual Foo() {{
public virtual voidvoid Foo() {
override void Foo()
base.Foo();
Console.WriteLine("Derived.Foo");
} Console.WriteLine("Derived.Foo");
} }
}

Conditional Compilation
#define, #undef
#if, #elif, #else, #endif
Simple boolean logic
Conditional methods
public class Debug
{
[Conditional("Debug")]
public static void Assert(bool cond, String s) {
if (!cond) {
throw new AssertionException(s);
}
}
}

Unsafe Code
Platform interoperability covers most cases
Unsafe code
Low-level code “within the box”
Enables unsafe casts, pointer arithmetic
Declarative pinning
Fixed statement
Basically “inline C”
unsafe void Foo() {
char* buf = stackalloc char[256];
for (char* p = buf; p < buf + 256; p++) *p = 0;
...
}

Unsafe Code
class FileStream: Stream
{
int handle;

public unsafe int Read(byte[] buffer, int index, int count) {
int n = 0;
fixed (byte* p = buffer) {
ReadFile(handle, p + index, count, &n, null);
}
return n;
}

[dllimport("kernel32", SetLastError=true)]
static extern unsafe bool ReadFile(int hFile,
void* lpBuffer, int nBytesToRead,
int* nBytesRead, Overlapped* lpOverlapped);
}

More Information
http://msdn.microsoft.com/net
Download .NET SDK and documentation
http://msdn.microsoft.com/events/pdc
Slides and info from .NET PDC
news://msnews.microsoft.com
microsoft.public.dotnet.csharp.general

Introduction to c#

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