#1 Introduction to C#

#1 Introduction to C# - Introduction to C# Anders Hejlsberg...

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Unformatted text preview: Introduction to C# Anders Hejlsberg Anders Distinguished Engineer Developer Division Microsoft Corporation C# – The Big Ideas C# The first component oriented The language in the C/C++ family language Everything really is an object Next generation robust and Next durable software durable Preservation of investment C# – The Big Ideas C# A component oriented language C# is the first “component oriented” C# language in the C/C++ family language 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 C# – The Big Ideas C# Everything really is an object Traditional views C# unifies with no performance cost C++, Java: Primitive types are “magic” and do C++, not interoperate with objects not Smalltalk, Lisp: Primitive types are objects, but Smalltalk, at great performance cost at Deep simplicity throughout system Improved extensibility and reusability New primitive types: Decimal, SQL… Collections, etc., work for all types Collections, types C# – The Big Ideas C# Robust and durable software Garbage collection Exceptions Error handling is not an afterthought Type-safety No memory leaks and stray pointers No uninitialized variables, unsafe casts Versioning Pervasive versioning considerations in Pervasive all aspects of language design all C# – The Big Ideas C# Preservation of Investment C++ heritage Interoperability Namespaces, enums, unsigned types, pointers Namespaces, (in unsafe code), etc. (in No unnecessary sacrifices What software is increasingly about MS C# implementation talks to XML, SOAP, MS COM, DLLs, and any .NET language COM, Millions of lines of C# code in .NET Short learning curve Increased productivity Hello World Hello using System; class Hello { static void Main() { Console.WriteLine("Hello world"); } } C# Program Structure C# Namespaces Type declarations Classes, structs, interfaces, enums, Classes, and delegates and Members Contain types and other namespaces Constants, fields, methods, properties, indexers, Constants, events, operators, constructors, destructors events, Organization No header files, code written “in-line” No declaration order dependence C# Program Structure C# 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 Type 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 s 123 "Hello world" Type System Type Value types Primitives Enums Structs y; } int i; i nt i; enum State { Off, On } struct Point { int x, Reference types Classes class Foo: Bar, IFoo Interfaces interface IFoo: IBar i nterface IFoo: IBar Arrays string a = new string[10]; {...} {...} Predefined Types Predefined C# predefined types Reference Signed Unsigned Unsigned Character Floating-point Logical object, string sbyte, short, int, long byte, ushort, uint, ulong char float, double, decimal bool Predefined types are simply aliases Predefined for system-provided types for For example, int == System.Int32 Classes Classes Single inheritance Multiple interface implementation Class members Constants, fields, methods, properties, Constants, indexers, events, operators, constructors, destructors constructors, Static and instance members Nested types Member access public, protected, internal, private Structs Structs Like classes, except Ideal for light weight objects Stored in-line, not heap allocated Assignment copies data, not reference No inheritance 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 Classes class CPoint { int x, y; ... } struct SPoint { int x, y; ... } CPoint cp = new CPoint(10, 20); SPoint sp = new SPoint(10, 20); sp 10 20 cp CPoint 10 20 Interfaces Interfaces Multiple inheritance Can contain methods, properties, Can indexers, and events indexers, Private interface implementations interface IDataBound { void Bind(IDataBinder binder); } class EditBox: Control, IDataBound { void IDataBound.Bind(IDataBinder binder) {...} } Enums 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 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 Unified Everything is an object All types ultimately inherit from object Any piece of data can be stored, Any transported, and manipulated with no extra work extra object Stream MemoryStream Hashtable FileStream int double Unified Type System Unified 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 System.Int32 o j 123 123 Unified Type System Unified 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 Component What defines a component? C# has first class support Properties, methods, events Integrated help and documentation Design-time information Not naming patterns, adapters, etc. Not external files Components are easy to build Components and consume and Properties 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 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; ListBox listBox = new ListBox(); Repaint(); listBox[0] = "hello"; } Console.WriteLine(listBox[0]); } } Events Sourcing 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 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 Attributes How do you associate information How with types and members? with Traditional solutions Documentation URL for a class Transaction context for a method XML persistence mapping Add keywords or pragmas to language Use external files, e.g., .IDL, .DEF C# solution: Attributes Attributes Attributes public class OrderProcessor { [WebMethod] public void SubmitOrder(PurchaseOrder order) {...} } [XmlRoot("Order", Namespace="urn:acme.b2b­schema.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 Attributes can be Completely extensible Simply a class that inherits from Simply System.Attribute System.Attribute Type-safe Attached to types and members Examined at run-time using reflection Arguments checked at compile-time Extensive use in .NET Framework XML, Web Services, security, serialization, XML, component model, COM and P/Invoke interop, code configuration… code XML Comments XML 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 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 foreach 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 Parameter 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 Operator First class user-defined data types Used in base class library Used in UI library Decimal, DateTime, TimeSpan Unit, Point, Rectangle Used in SQL integration SQLString, SQLInt16, SQLInt32, SQLString, SQLInt64, SQLBool, SQLMoney, SQLNumeric, SQLFloat… SQLNumeric, Operator Overloading Operator 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 Versioning Problem in most languages C# allows intent to be expressed C++ and Java produce fragile base classes C++ Users unable to express versioning intent Methods are not virtual by default C# keywords “virtual”, “override” and “new” C# provide context provide C# can't guarantee versioning Can enable (e.g., explicit override) Can encourage (e.g., smart defaults) Versioning Versioning class Base class Base // version 2 // version 1 { } public virtual void Foo() { Console.WriteLine("Base.Foo"); } } class Derived: Base // version 2b // version 2a // version 1 { public virtual void Foo() { public override void Foo() { new public virtual void Foo() { Console.WriteLine("Derived.Foo"); base.Foo(); } Console.WriteLine("Derived.Foo"); }} } Conditional Compilation Conditional #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 Unsafe Platform interoperability covers most cases Unsafe code Declarative pinning Low-level code “within the box” Enables unsafe casts, pointer arithmetic 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 Unsafe 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 More 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 ...
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This note was uploaded on 06/14/2011 for the course COMPUTER 091 taught by Professor Rajivsir during the Summer '11 term at MIT.

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