Posts Tagged ‘ C# ’

The power of closures in C# 2.0

Martin Fowler (obligitary Fowlbot namedrop) recently blogged about the power of closures in languages that support them. It’s worth remembering that C# 2.0 has true closure support in the form of anonymous delegates. This includes reading and modifying variables outside the context of the closure – unlike Java’s anonymous inner classes.

Just for kicks, I’ve rewritten all of the examples Martin’s Ruby examples in C# 2.0. This makes use of the improved APIs in .NET 2.0 pointed out by Zohar.

Ruby C# 2.0 
def managers(emps)
return emps.select {|e| e.isManager}
end
 
public List<Employee> Managers(List<Employee> emps) {
return emps.FindAll(delegate(Employee e) {
return e.IsManager;
}
}
 
def highPaid(emps)
threshold = 150
return emps.select {|e| e.salary > threshold}
end
 
public List<Employee> HighPaid(List<Employee> emps) {
int threshold = 150;
return emps.FindAll(delegate(Employee e) {
return e.Salary > threshold;
});
}
 
def paidMore(amount)
return Proc.new {|e| e.salary > amount}
end
 
public Predicate<Employee> PaidMore(int amount) {
return delegate(Employee e) {
return e.Salary > amount;
}
}
 
highPaid = paidMore(150)
john = Employee.new
john.salary = 200
print highPaid.call(john)
 
Predicate<Employee> highPaid = PaidMore(150);
Employee john = new Employee();
john.Salary = 200;
Console.WriteLine(highPaid(john));

The code difference between the languages isn’t that difference. The C# 2.0 code is obviously longer (though not a lot) because:

  • C# 2.0 is staticly typed (let’s not get started on the static vs dynamic debate).
  • C# 2.0 requires the ‘delegate’ keyword.
  • Ruby allows you to ignore the ‘return’ keyword.

You can try this stuff out yourself by playing with Visual C# Express.

2004
09/16
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23 comments

NMock article in MSDN Magazine

An article about NMock has appeared in the October issue of MSDN Magazine. Chuffed :)

Mock Objects to the Rescue! Test Your .NET Code with NMock

2004
09/16
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OT2004 : Generic Mechanisms in Software Engingeering

This workshop, hosted by Simon Davies, and chums from Microsoft (with a bit of Bruce Anderson), was a thinking excercise about the pros and cons of some of the language features of C# (and conveniently also Java) including generic types, attributes and dynamic code generation.

We were given some sample scenarios to which we had to contrast the approaches of using these features in isolation and combined together, taking into account ease of development, runtime performance, flexibility, maintainability and simplicity:
* Creating a strongly typed list.
* Serializing objects to XML (a subject I’m familiar with).
* CRUD persistence of domain objects to a database.

This was quite thought provoking. While it was very easy to see the advantages of using generics to implement a strongly typed list, experimenting with all the different approaches was a fun exercise. Code generation may be less simple but offers better runtime performance.

It was fun brainstorming ideas with developers from different backgrounds and seeing which approaches appealed to them.

I was also shown the anonymous delegate feature in the next version of C#. Mmmm closures…

// usage
int totalAge = 0;
peopleFinder.All(delegate(Person person) {
totalAge += person.Age;
});

// implementation
class PersonFinder {

public delegate PersonDelegate(Person person);

public void All(PersonDelegate delegate) {
some magic iteration code {
Person person = ...;
delegate(person);
}
}

}

Now for a staticly typed language, that’s a lot cleaner than I was expecting.

This is something I’m really excited about as it’s the style of development I use all the time in Java, without all the syntactic cruft of anonymous inner classes. And I’m sure it’ll appeal to all the Ruby/Smalltalkers out there.

Something else I learned is that (unlike Java 1.5), generic definitions are available at runtime.

Plenty more info in the C# 2.0 specification.

2004
03/31
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4 comments

How to do Dynamic Proxies in C#

Background: A dynamic proxy dynamically generates a class at runtime that conforms to a particular interface, proxying all invocations to a single ‘generic’ method.

Earlier, Stellsmi asked if it’s possible to do this in .NET (it’s a standard part of Java). Seeing as it’s the second time I’ve talked about it in as many days, I reckon it’s worth blogging…

As far as I know, there are two ways to do this:

* Using the magical RealProxy class that monkeys with the context (whatever that means). This requires that the object that is being proxied must extend ContextBound.
* Using Reflection.Emit to generate a new class at runtime that overrides/implements the necessary methods and dispatches invocations to a generic handler. This can implement an interface or override any virtual method.

The first approach is pretty trivial, but it locks you into the fact that you can only proxy objects that extend ContextBound. Not ideal as this pulls a lot of stuff into your class you don’t necessarily need and prevents you from inheriting something else.

The second approach is more suitable, less intrusive, but not pretty to write as it involves writing low-level IL op-codes. However, I did this already in NMock and at GeekNight, Steve and Jon lovingly decoupled the ClassGenerator from the core of NMock, so you can create generic dynamic proxies. So now it’s easy to create a proxy.

h3. Example

Here’s an interface you want to create a dynamic proxy for:

interface IFoo {
string DoStuff(int n);
}

Note:

* You can use one invocation handler to handle all method calls in the interface. The example above only has one method for clarity.
* This doesn’t have to be an interface. It could be a class, so long as the methods you want handle are all marked virtual (sigh).
* You can do the same thing for properties as well as methods.

To create the proxy, you need to create an implementation of IInvocationHandler. This is called any time a method is invoked on the proxy.

class MyHandler : IInvocationHandler {
public object Invoke(string methodName, param object[] args) {
return "hello from " + methodName;
}
}

Notes:

* The name of the method being called and parameters passed in are passed to this handler.
* Whatever is returned by the Invoke() method is returned by the proxy.
* If the method is of type void, just return null.

Finally, you need to generate the proxy itself so you can actually use the damn thing:

ClassGenerator generator = new ClassGenerator(
typeof(Foo), new MyHandler()  );
IFoo fooProxy = (IFoo)generator.Generate();

string result = fooProxy.DoStuff(2); // returns "hello from DoStuff"

Ermm and that’s it! Use your dynamic proxy like it’s a real class.

ClassGenerator is part of the NMock library. Use it for AOP style interceptors, decorators, stubbing, mocking :), whatever.

Brain rumblings… Hmm… maybe that should be a delegate instead… maybe I should revisit some stuff…

2004
02/12
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14 comments

NMock 1.0

After many months of little changes, we deemed NMock production quality. It stabilised quickly many months ago and has changed very little since.

Documentation is somewhat sparse – contributions welcome!

“http://nmock.truemesh.com/&#8221;:http://nmock.truemesh.com/

2003
06/13
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1 comment