LINQ in Norway
PDC2008 - Type System Changes with CLR 4.0

PDC 2008 - C# Futures

Again, Anders Hejlsberg had a great session at #pdc2008. This time about C# 4.0 and C# 5.0!

C# 1.0 was the core about OO, C# 2.0 added generics. With C# 3.0 is the first version with new language features - LINQ, and this is expands with the future versions. C# is a multi-paradigm language. Of course, it's an OO language (since 1.0), since 3.0 it can also be used as functional language. The main areas of enhancements are in these areas:

  • declarative
  • dynamic
  • concurrent

Microsoft is doing a shift in regard to C# and VB to recognize reality. Features from C# are brought into VB, and features from VB into C# - because the demand is here!

C# 4.0 adds dynamic programming. With this it is easy to call not only .NET objects but also easily COM objects, JavaScript, Python...
The enhancements can be grouped into these areas:

  • dynamic keyword
  • optional and named parameters
  • co- and contra variance

With the new dynamic keyword, a variable can be declared in C# that references a object that is created during runtime, e.g. from COM or JavaScript.

dynamic calc = GetCalculator();
int sum = calc.Add(10, 20);
Every method that is invoked on a dynamic object returns a dynamic result that is dynamically cast to the type the return variable is declared (e.g. an int in the example). A great feature here is the syntax looks the same, no matter if the calculator is a COM object, JavaScript, Python or Ruby. Binders for each of these variants are available, and custom binders can be written as well.
Using C# it is also possible to create dynamic runtime-objects by implementing the interface IDynamicObject or deriving from the base class DynamicObject.

A many times requested feature that is available with C# 4.0 is optional and named parameters. Instead of defining several overloads, optional parameters can be defined:

StreamReader OpenTextFile(
   string path,
   Encoding encoding = null,
   bool detectEncoding = true,
   int bufferSize = 1024);
this can be called wih only the mandatory parameter:
OpenTextFile("foo.txt");
and also with named arguments:
OpenTextfile("foo.txt", bufferSize : 4096);
Of course, named arguments must be after the mandatory parameters.

Optional and named parameters have a great COM Interop story. No more ref missing parameters. "It took 10 years to get back where we were".

Covariance and contra-variance is another new feature. co-variance or contra-variance information can be added to generics, e.g. and . means that T can be used only in output positions, only in input positions. Existing interfaces and delegates such as IEnumerably and IComparable are changed to the new notation. A blog entry with samples about this feature follows here!

Anders also demonstrated C# 5.0 features. C# 5.0 opens up the compiler to offer modern ways for meta-programming - compiler as a service!

More information about C# futures:http://code.msdn.microsoft.com/csharpfuture

Christian

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