C#

Fresh from Twitter, here are some ways to use attributes in C# that you might not know ...

Did you know you can put attributes on method parameters ...

public string MyMethod([MyCustomAttribute] int id)
{
    // ...
}

Did you know you can specify an attribute on the return of a method ...

[return: CrazyAttributeOnAReturnMethod(WithAParameterOfItsOwn = true)]
public string MyMethod(int id)
{
    // ...
}

For the record: I knew the first, but not the second ...

A lot of the discussion about .NET 4.0 is revolving around the introduction of co-variance and contra-variance for generic types.

It's important to remember, though, that these concepts aren't entirely new - there has been some support for variance built into .NET for some time.

For example, consider this snippet of code:

    public Form1()
    {
        InitializeComponent();
 
        textBox1.KeyPress += Handler;
        button1.Click += Handler;
 
        textBox1.KeyPress += new KeyPressEventHandler(Handler);
        button1.Click += new EventHandler(Handler);

I had an interesting conversation with a friend earlier this week, over when to use the var keyword in C# 3.0.

He and a colleague had divergent views, one passionately arguing it should be used whenever possible, and the other just as passionate in his view that it should never be used.

Of all the new features in C# 3.0, Lambda expressions have to be one of my favourites.

One non-obvious way that they can be used is as event handlers, in just the way that anonymous delegates could be.

I'm sure that most of you know that you can't call methods on a null reference, so you'll expect that this code will fire a nasty exception:

IPath p = null;
int l = p.Length();

Except, it doesn't.

Why?

Over the past few weeks, I've been spending a great deal of time getting to grips with the new features available in .NET 3.5, especially the new syntax supported by C# 3.0.