The Creation of C#

piteousnessbutterSoftware and s/w Development

Jul 14, 2012 (4 years and 9 months ago)

301 views

CompRef8 / C# 3.0: The Complete Reference / Schildt / 841-8
1
The Creation of C#
C
# is Microsoft’s premier language for .NET development. It leverages time-tested
features with cutting-edge innovations and provides a highly usable, efficient way
to write programs for the modern enterprise computing environment. It is, by any
measure, one of the most important languages of the 21st century.
The purpose of this chapter is to place C# into its historical context, including the forces
that drove its creation, its design philosophy, and how it was influenced by other computer
languages. This chapter also explains how C# relates to the .NET Framework. As you will
see, C# and the .NET Framework work together to create a highly refined programming
environment.
C#’s Family Tree
Computer languages do not exist in a void. Rather, they relate to one another, with each new
language influenced in one form or another by the ones that came before. In a process akin to
cross-pollination, features from one language are adapted by another, a new innovation is
integrated into an existing context, or an older construct is removed. In this way, languages
evolve and the art of programming advances. C# is no exception.
C# inherits a rich programming legacy. It is directly descended from two of the world’s
most successful computer languages: C and C++. It is closely related to another: Java.
Understanding the nature of these relationships is crucial to understanding C#. Thus, we
begin our examination of C# by placing it in the historical context of these three languages.
C: The Beginning of the Modern Age of Programming
The creation of C marks the beginning of the modern age of programming. C was invented
by Dennis Ritchie in the 1970s on a DEC PDP-11 that used the UNIX operating system.
While some earlier languages, most notably Pascal, had achieved significant success, C
established the paradigm that still charts the course of programming today.
C grew out of the structured programming revolution of the 1960s. Prior to structured
programming, large programs were difficult to write because the program logic tended to
degenerate into what is known as “spaghetti code,” a tangled mass of jumps, calls, and
returns that is difficult to follow. Structured languages addressed this problem by adding
well-defined control statements, subroutines with local variables, and other improvements.
Through the use of structured techniques programs became better organized, more reliable,
and easier to manage.
3
CHAPTER
ch01.indd 3
ch01.indd 3
11/13/2008 2:07:09 PM
11/13/2008 2:07:09 PM
CompRef8 / C# 3.0: The Complete Reference / Schildt / 841-8

4
P a r t I: T h e C# L a n g u a g e
Although there were other structured languages at the time, C was the first to successfully
combine power, elegance, and expressiveness. Its terse, yet easy-to-use syntax coupled with
its philosophy that the programmer (not the language) was in charge quickly won many
converts. It can be a bit hard to understand from today’s perspective, but C was a breath of
fresh air that programmers had long awaited. As a result, C became the most widely used
structured programming language of the 1980s.
However, even the venerable C language had its limits. One of the most troublesome
was its inability to handle large programs. The C language hits a barrier once a project
reaches a certain size, and after that point, C programs are difficult to understand and
maintain. Precisely where this limit is reached depends upon the program, the programmer,
and the tools at hand, but there is always a threshold beyond which a C program becomes
unmanageable.
The Creation of OOP and C++
By the late 1970s, the size of many projects was near or at the limits of what structured
programming methodologies and the C language could handle. To solve this problem, a
new way to program began to emerge. This method is called object-oriented programming
(OOP). Using OOP, a programmer could handle much larger programs. The trouble was
that C, the most popular language at the time, did not support object-oriented programming.
The desire for an object-oriented version of C ultimately led to the creation of C++.
C++ was invented by Bjarne Stroustrup beginning in 1979 at Bell Laboratories in Murray
Hill, New Jersey. He initially called the new language “C with Classes.” However, in 1983 the
name was changed to C++. C++ contains the entire C language. Thus, C is the foundation
upon which C++ is built. Most of the additions that Stroustrup made to C were designed to
support object-oriented programming. In essence, C++ is the object-oriented version of C. By
building upon the foundation of C, Stroustrup provided a smooth migration path to OOP.
Instead of having to learn an entirely new language, a C programmer needed to learn only
a few new features before reaping the benefits of the object-oriented methodology.
C++ simmered in the background during much of the 1980s, undergoing extensive
development. By the beginning of the 1990s, C++ was ready for mainstream use, and its
popularity exploded. By the end of the decade, it had become the most widely used
programming language. Today, C++ is still the preeminent language for the development of
high-performance system code.
It is critical to understand that the invention of C++ was not an attempt to create an
entirely new programming language. Instead, it was an enhancement to an already highly
successful language. This approach to language development—beginning with an existing
language and moving it forward—established a trend that continues today.
The Internet and Java Emerge
The next major advance in programming languages is Java. Work on Java, which was
originally called Oak, began in 1991 at Sun Microsystems. The main driving force behind
Java’s design was James Gosling. Patrick Naughton, Chris Warth, Ed Frank, and Mike
Sheridan also played a role.
Java is a structured, object-oriented language with a syntax and philosophy derived from
C++. The innovative aspects of Java were driven not so much by advances in the art of
programming (although some certainly were), but rather by changes in the computing
environment. Prior to the mainstreaming of the Internet, most programs were written,
ch01.indd 4
ch01.indd 4
11/13/2008 2:07:09 PM
11/13/2008 2:07:09 PM
CompRef8 / C# 3.0: The Complete Reference / Schildt / 841-8
PART I
C h a p t e r 1: T h e C r e a t i o n o f C#
5
PART I
PART I
compiled, and targeted for a specific CPU and a specific operating system. While it has always
been true that programmers like to reuse their code, the ability to port a program easily from
one environment to another took a backseat to more pressing problems. However, with the
rise of the Internet, in which many different types of CPUs and operating systems are
connected, the old problem of portability reemerged with a vengeance. To solve the problem
of portability, a new language was needed, and this new language was Java.
Although the single most important aspect of Java (and the reason for its rapid acceptance)
is its ability to create cross-platform, portable code, it is interesting to note that the original
impetus for Java was not the Internet, but rather the need for a platform-independent
language that could be used to create software for embedded controllers. In 1993, it became
clear that the issues of cross-platform portability found when creating code for embedded
controllers are also encountered when attempting to create code for the Internet. Remember:
the Internet is a vast, distributed computing universe in which many different types of
computers live. The same techniques that solved the portability problem on a small scale
could be applied to the Internet on a large scale.
Java achieved portability by translating a program’s source code into an intermediate
language called bytecode. This bytecode was then executed by the Java Virtual Machine
(JVM). Therefore, a Java program could run in any environment for which a JVM was
available. Also, since the JVM is relatively easy to implement, it was readily available for
a large number of environments.
Java’s use of bytecode differed radically from both C and C++, which were nearly
always compiled to executable machine code. Machine code is tied to a specific CPU and
operating system. Thus, if you wanted to run a C/C++ program on a different system, it
needed to be recompiled to machine code specifically for that environment. Therefore, to
create a C/C++ program that would run in a variety of environments, several different
executable versions of the program would be needed. Not only was this impractical, it was
expensive. Java’s use of an intermediate language was an elegant, cost-effective solution.
It is also a solution that C# would adapt for its own purposes.
As mentioned, Java is descended from C and C++. Its syntax is based on C, and its object
model is evolved from C++. Although Java code is neither upwardly nor downwardly
compatible with C or C++, its syntax is sufficiently similar that the large pool of existing
C/C++ programmers could move to Java with very little effort. Furthermore, because Java
built upon and improved an existing paradigm, Gosling, et al., were free to focus their
attention on the new and innovative features. Just as Stroustrup did not need to “reinvent
the wheel” when creating C++, Gosling did not need to create an entirely new language
when developing Java. Moreover, with the creation of Java, C and C++ became an accepted
substrata upon which to base a new computer language.
The Creation of C#
While Java has successfully addressed many of the issues surrounding portability in the
Internet environment, there are still features that it lacks. One is cross-language interoperability,
also called mixed-language programming. This is the ability for the code produced by one
language to work easily with the code produced by another. Cross-language interoperability
is needed for the creation of large, distributed software systems. It is also desirable for
programming software components because the most valuable component is one that can
be used by the widest variety of computer languages, in the greatest number of operating
environments.
ch01.indd 5
ch01.indd 5
11/13/2008 2:07:09 PM
11/13/2008 2:07:09 PM
CompRef8 / C# 3.0: The Complete Reference / Schildt / 841-8

6
P a r t I: T h e C# L a n g u a g e
Another feature lacking in Java is full integration with the Windows platform. Although
Java programs can be executed in a Windows environment (assuming that the Java Virtual
Machine has been installed), Java and Windows are not closely coupled. Since Windows is
the most widely used operating system in the world, lack of direct support for Windows is a
drawback to Java.
To answer these and other needs, Microsoft developed C#. C# was created at Microsoft
late in the 1990s and was part of Microsoft’s overall .NET strategy. It was first released in its
alpha version in the middle of 2000. C#’s chief architect was Anders Hejlsberg. Hejlsberg is
one of the world’s leading language experts, with several notable accomplishments to his
credit. For example, in the 1980s he was the original author of the highly successful and
influential Turbo Pascal, whose streamlined implementation set the standard for all future
compilers.
C# is directly related to C, C++, and Java. This is not by accident. These are three of
the most widely used—and most widely liked—programming languages in the world.
Furthermore, at the time of C#’s creation, nearly all professional programmers knew C, C++,
and/or Java. By building C# upon a solid, well-understood foundation, C# offered an easy
migration path from these languages. Since it was neither necessary nor desirable for Hejlsberg
to “reinvent the wheel,” he was free to focus on specific improvements and innovations.
The family tree for C# is shown in Figure 1-1. The grandfather of C# is C. From C, C#
derives its syntax, many of its keywords, and its operators. C# builds upon and improves
the object model defined by C++. If you know C or C++, then you will feel at home with C#.
C# and Java have a bit more complicated relationship. As explained, Java is also
descended from C and C++. It too shares the C/C++ syntax and object model. Like Java, C#
is designed to produce portable code. However, C# is not descended from Java. Instead, C#
and Java are more like cousins, sharing a common ancestry, but differing in many important
ways. The good news, though, is that if you know Java, then many C# concepts will be
familiar. Conversely, if in the future you need to learn Java, then many of the things you
learn about C# will carry over.
C# contains many innovative features that we will examine at length throughout the
course of this book, but some of its most important relate to its built-in support for software
components. In fact, C# has been characterized as being a component-oriented language
because it contains integral support for the writing of software components. For example,
F
IGURE
1-1
The C# family tree
ch01.indd 6
ch01.indd 6
11/13/2008 2:07:10 PM
11/13/2008 2:07:10 PM
CompRef8 / C# 3.0: The Complete Reference / Schildt / 841-8
PART I
C h a p t e r 1: T h e C r e a t i o n o f C#
7
PART I
PART I
C# includes features that directly support the constituents of components, such as
properties, methods, and events. However, C#’s ability to work in a secure, mixed-language
environment is perhaps its most important component-oriented feature.
The Evolution of C#
Since its original 1.0 release, C# has been evolving at a rapid pace. Not long after C# 1.0,
Microsoft released version 1.1. It contained many minor tweaks but added no major
features. However, the situation was much different with the release of C# 2.0.
C# 2.0 was a watershed event in the lifecycle of C# because it added many new features,
such as generics, partial types, and anonymous methods, that fundamentally expanded
the scope, power, and range of the language. Version 2.0 firmly put C# at the forefront of
computer language development. It also demonstrated Microsoft’s long-term commitment
to the language.
The next major release of C# was 3.0, and this is the version of C# described by this book.
Because of the many new features added by C# 2.0, one might have expected the development
of C# to slow a bit, just to let programmers catch up, but this was not the case. With the release
of C# 3.0, Microsoft once again put C# on the cutting edge of language design, this time
adding a set of innovative features that redefined the programming landscape. Here is
a list of what 3.0 has added to the language:
• Anonymous types
• Auto-implemented properties
• Extension methods
• Implicitly typed variables
• Lambda expressions
• Language-integrated query (LINQ)
• Object and collection initializers
• Partial methods
Although all of these features are important and have significant impact on the language,
the two that are the most exciting are language-integrated query (LINQ) and lambda
expressions. LINQ enables you to write database-style queries using C# programming
elements. However, the LINQ syntax is not limited to only databases. It can also be used
with arrays and collections. Thus, LINQ offers a new way to approach several common
programming tasks. Lambda expressions are often used in LINQ expressions, but can also be
used elsewhere. They implement a functional-style syntax that uses the lambda operator =>.
Together, LINQ and lambda expressions add an entirely new dimension to C# programming.
Throughout the course of this book, you will see how these features are revolutionizing the
way that C# code is written.
How C# Relates to the .NET Framework
Although C# is a computer language that can be studied on its own, it has a special
relationship to its runtime environment, the .NET Framework. The reason for this is
twofold. First, C# was initially designed by Microsoft to create code for the .NET
ch01.indd 7
ch01.indd 7
11/13/2008 2:07:10 PM
11/13/2008 2:07:10 PM
CompRef8 / C# 3.0: The Complete Reference / Schildt / 841-8

8
P a r t I: T h e C# L a n g u a g e
Framework. Second, the libraries used by C# are the ones defined by the .NET Framework.
Thus, even though it is theoretically possible to separate C# the language from the .NET
environment, in practice the two are closely linked. Because of this, it is important to have a
general understanding of the .NET Framework and why it is important to C#.
What Is the .NET Framework?
The .NET Framework defines an environment that supports the development and execution
of highly distributed, component-based applications. It enables differing computer languages
to work together and provides for security, program portability, and a common programming
model for the Windows platform. As it relates to C#, the .NET Framework defines two very
important entities. The first is the Common Language Runtime (CLR). This is the system that
manages the execution of your program. Along with other benefits, the Common Language
Runtime is the part of the .NET Framework that enables programs to be portable, supports
mixed-language programming, and provides for secure execution.
The second entity is the .NET class library. This library gives your program access to the
runtime environment. For example, if you want to perform I/O, such as displaying something
on the screen, you will use the .NET class library to do it. If you are new to programming,
then the term class may be new. Although it is explained in detail later in this book, for now
a brief definition will suffice: a class is an object-oriented construct that helps organize
programs. As long as your program restricts itself to the features defined by the .NET class
library, your programs can run anywhere that the .NET runtime system is supported. Since
C# automatically uses the .NET Framework class library, C# programs are automatically
portable to all .NET environments.
How the Common Language Runtime Works
The Common Language Runtime manages the execution of .NET code. Here is how it
works: When you compile a C# program, the output of the compiler is not executable code.
Instead, it is a file that contains a special type of pseudocode called Microsoft Intermediate
Language (MSIL). MSIL defines a set of portable instructions that are independent of any
specific CPU. In essence, MSIL defines a portable assembly language. One other point:
although MSIL is similar in concept to Java’s bytecode, the two are not the same.
It is the job of the CLR to translate the intermediate code into executable code when a
program is run. Thus, any program compiled to MSIL can be run in any environment for
which the CLR is implemented. This is part of how the .NET Framework achieves portability.
Microsoft Intermediate Language is turned into executable code using a JIT compiler.
“JIT” stands for “Just-In-Time.” The process works like this: When a .NET program is
executed, the CLR activates the JIT compiler. The JIT compiler converts MSIL into native
code on demand as each part of your program is needed. Thus, your C# program actually
executes as native code even though it is initially compiled into MSIL. This means that your
program runs nearly as fast as it would if it had been compiled to native code in the first
place, but it gains the portability benefits of MSIL.
In addition to MSIL, one other thing is output when you compile a C# program:
metadata. Metadata describes the data used by your program and enables your code to
interact easily with other code. The metadata is contained in the same file as the MSIL.
ch01.indd 8
ch01.indd 8
11/13/2008 2:07:10 PM
11/13/2008 2:07:10 PM
CompRef8 / C# 3.0: The Complete Reference / Schildt / 841-8
PART I
C h a p t e r 1: T h e C r e a t i o n o f C#
9
PART I
PART I
Managed vs. Unmanaged Code
In general, when you write a C# program, you are creating what is called managed code.
Managed code is executed under the control of the Common Language Runtime as just
described. Because it is running under the control of the CLR, managed code is subject to
certain constraints—and derives several benefits. The constraints are easily described and
met: the compiler must produce an MSIL file targeted for the CLR (which C# does) and use
the .NET class library (which C# does). The benefits of managed code are many, including
modern memory management, the ability to mix languages, better security, support for
version control, and a clean way for software components to interact.
The opposite of managed code is unmanaged code. Unmanaged code does not execute
under the Common Language Runtime. Thus, all Windows programs prior to the creation of
the .NET Framework use unmanaged code. It is possible for managed code and unmanaged
code to work together, so the fact that C# generates managed code does not restrict its ability
to operate in conjunction with preexisting programs.
The Common Language Specification
Although all managed code gains the benefits provided by the CLR, if your code will be
used by other programs written in different languages, then for maximum usability, it should
adhere to the Common Language Specification (CLS). The CLS describes a set of features
that different .NET-compatible languages have in common. CLS compliance is especially
important when creating software components that will be used by other languages. The
CLS includes a subset of the Common Type System (CTS). The CTS defines the rules
concerning data types. Of course, C# supports both the CLS and the CTS.
ch01.indd 9
ch01.indd 9
11/13/2008 2:07:10 PM
11/13/2008 2:07:10 PM