What’s New in Visual C# 4.0

Visual C# version 4.0 offers new features that make it easier for you to work in dynamic programming scenarios. Besides dynamic programming, you have support for optional and named parameters, better COM interop support, and contra-variance and covariance. This article will show you how each of these features work and provide suggestions of

how they can be applied to help you be more productive.

To help you follow the path of C#, this article looks at the history of C#, today’s use of C#, and helps you understand the future of C# and what the language intends to provide for you. After you understand the theme of C# 4.0, you’ll learn about the new features of C# 4.0. Finally, this article will show you how to create a dynamic object of your own with late-bound calls to dynamic methods based on conventions.

C#: Then and Now

The previous major versions of C# were 1.0, 2.0, and 3.0. There was a minor version 1.1 in April of 2003, but it didn’t significantly change the theme of the 1.0 release. I’ll discuss these versions in the following sections.

Microsoft first announced C# on June 16th 2000. It was the first high-level programming language that was built specifically to target the .NET Common Language Runtime. C# 1.0 grew its heritage from C++, but borrowed features from languages such as Delphi, Java, and others. In C# 1.0, Microsoft planned to provide an object-oriented, component-based language that was very simple to use. When Microsoft released C# 1.0 to manufacturing on February 13th 2002, it was an immediate hit and steadily grew in popularity.

When C# 2.0 rolled around, Microsoft finally added all of the features that should have been in C# 1.0. For example, generics was huge and is an important part of .NET development today. C# 2.0 also introduced anonymous methods, iterators, and nullable types. An interesting addition to C# 2.0, nullable types was a pre-cursor feature for what was coming in the next version, focusing on data.

Most developers work with data, which was the primary theme of C# 3.0. The largest C# 3.0 language addition was Language Integrated Query (LINQ). Most other language features added in C# 3.0 were primarily to support LINQ, but the new features; including implicitly typed local variables, anonymous types, object and collection initializers, lambdas, and extension methods, can have value on their own in development that doesn’t involve LINQ.

The next version of C# will be 4.0, which is the focus of this article. C# 4.0 will primarily focus on dynamic programming. The following sections of this article explain the dynamic programming features of C# 4.0 as well as other new features such as optional/named parameters and covariance/contravariance.

Why Dynamic Programming?

The dynamic programming story in C# can fall into fulfilling categories of need in the way of multiple-language integration, simpler reflection, access to HTML DOM in Web scenarios, and easier COM interop. Some of these categories of need might not apply to your particular situation, and that’s okay because there isn’t anything that says that you have to use a language feature just because it’s there. Therefore, I’ll give you an idea of how someone with a specific need might find value in C# 4.0 dynamic programming.

"

C# 4.0 will primarily focus on dynamic programming.

"

Most C# developers use multiple tools in a single application to accomplish complex tasks. If you’re writing WPF desktop applications, you’re using C# and XAML. It is quite possible that you might find some open source code that solves a problem, but it might be written in another language such as VB or F#. One of the benefits of .NET since its inception is the ability to have cross-language interoperability and the runtime is even called the “Common Language” Runtime (CLR). In recent years, Microsoft has created dynamic languages, such as IronRuby and IronPython, but developers don’t have an easy way to perform interop with dynamic languages. If you have this need, then you’ll welcome the ease with which C# dynamic programming makes interop between C# and dynamic languages possible.

When performing reflection to run a method on an object, there are several hoops to jump through, including obtaining a reference to an object type, getting a reference to a member info object, determining the type of bindings to use, and then invoking the member. While reflection has an undeniable coolness factor, it still feels like a hack and that’s where C# 4.0 dynamic methods can help. Later in this article, I’ll show you how to just call the object member.

If you write Silverlight applications, you might have the need today or in the future to access the HTML DOM containing your Silverlight control. C# dynamic programming makes this task easier.

Performing COM interop with C# has always been cumbersome; partly because of the need to write extra syntax for conversions, optional parameters, and more. This has left some C# developers with a touch of VB envy because VB has easier COM interop support. One of the purposes of dynamic programming in C# is to help the C# programmer write cleaner syntax in COM interop scenarios.

I’ve spent some time explaining some of the potential benefits of dynamic programming because it’s so new that the value might not jump out at you immediately. In following sections, I’ll share the how so that you can match it up with the why that you might care about. Before diving into dynamic programming, let’s look at a couple other new features of C# 4.0, optional and named parameters.

Optional Parameters

"

If you’re of the same mind, then you’ll probably be pleased that C# 4.0 supports optional parameters.

"

For many C# developers, the long wait for optional parameters is over with C# 4.0. An optional parameter lets you provide a default value and the caller has a choice of whether or not they want to provide an argument. In current and earlier versions of C#, you could simulate optional parameters like this:

// Overload with no parameterpublic static string SayHello(){    return "Hey, You!";}
// Overload with normal parameterpublic static string SayHello(string name){    return "Hey, " + name + "!";}

The SayHello method above is overloaded with both an empty parameter list and a parameter list with a single string parameter. To the user of this code, the name parameter appears to be optional and both of the following calls work fine:

// Name is optionalvar greetYou = SayHello();
// Can provide name if you wantvar greetJoe = SayHello("Joe");

If you had methods with more parameters and wanted to provide a more flexible coding experience, you would provide more overloads. Many developers have said that this is cumbersome and leaves more code to maintain. If you’re of the same mind, then you’ll probably be pleased that C# 4.0 supports optional parameters. The snippet below shows an optional parameter, replacing the previous two overloads:

// Method with optional parameterpublic static string SayHello(string name = "You"){    return "Hey, " + name + "!";}

As shown in the previous snippet, the syntax to call an optional parameter requires assigning a default value to the parameter. In the listing above, "You" will be assigned to name if the caller does not provide a value.

A feature related to optional parameters is named parameters, which is discussed next.

Named Parameters

One of the primary purposes of named parameters is that they resolve ambiguity between parameters. For example, the following method contains two parameters that are strings:

public static void AddClubMember(    string name,     string email = "",     DateTime? dateJoined = null){    // Not yet implemented}

The types of the first two parameters of the AddClubMember method above are both string, except that name is not optional, but email is optional. This example also demonstrates that you can default parameters to null.

AddClubMember(    email: "joe@dot.net",     name: "Joe",     dateJoined: DateTime.Now);}

The call to AddClubMember above uses named parameters where the name is the same as the parameter name in the method declaration with an appended colon. Notice that I’ve shuffled the parameter order to demonstrate that you can change the order of parameters.

"

Named parameters are particularly useful when you have multiple optional parameters of the same type.

"

Named parameters are particularly useful when you have multiple optional parameters of the same type. In that case, you name the parameter that you want to set, telling C# which parameter your argument matches. The code below demonstrates a problem where named parameters are necessary:

AddClubMember(    "joe@dot.net",     dateJoined: DateTime.Now);}

If you recall, the first parameter of the AddClubMember method is name, a required parameter of type string. Since the first argument above is a string, C# will match that argument to the name parameter. Clearly, the value above is an email address, which presents you with a logical error that won’t be detected at either compile time nor run time when that line executes.

Posted in: DOT NET