The new keyword "var":
It's both used in LINQ expressions and when using anonymous types (more about them later). It also can be used in any regular variable declaration and initialization, for example:
StringBuilder b = new StringBuilder();
b.Append("abc");
var varB = new StringBuilder();
varB.Append("abc");In the above example, var keyword was used instead of the StringBuilder class name in the second declaration. And the StringBuilder is used regularly. What worth mentioning is:
- Some ex-vb developers may think that var is the same as the vb6 Variant datatype, which will cause some performace degradation when calling methods due to late binding. This is not true. The compiler replaces the var with the type initialized in the RHS. So the compiler output of these 2 lines is the same:
StringBuilder b = new StringBuilder();var b = new StringBuilder();
We just saved some keystrokes :). - VS2008 has full intellisense support for var. as you can see in the screenshot:
LINQ:
Using Language Integrated Query with collections can make many of programming tasks easier, like searching for an object or objects in a collection that meet a certain criteria.
For example, if we have a List< string > and we want to find all strings that start with the letter 'S', this is the old way to do this :
List< string > found=new List< string >();
foreach (string s in items)
{
if (s.StartsWith("S"))
found.Add(s);
}
Using LINQ:
var found = from s in items
where s.StartsWith("S")
select s;
Ok, more value can be gained if you need to get them sorted by length:
var found = from s in items
where s.StartsWith("S")
orderby s.Length
select s;Some people may think that the 'var' keyword is what indicates a LINQ expression, but no, it's actually the 'from'.
A good place to think about using LINQ is where you usually use for and foreach.
LINQ is a new feature of C# v3.0 and VB.NET v9.0
Anonymous types:
I'll talk about Anonymous types usage in LINQ, although there are other cases when are useful.
In the above LINQ example, what if we don't need to get the result as a collection of complete objects of the original collection, and we just need one or two attributes (just as we can select just a few columns from a SQL database, not all columns from the table).
Anonymous types can be used in this case:
var found = from s in items
where s.StartsWith("S")
orderby s.Length
select new { value = s, length = s.Length };Here, we created a new type on the fly, it has 2 properties: value which is a string and length which is an integer.
But how to iterate on found when we don't know the type of the objects it holds (remember, it's anonymous). This is where var comes to be useful again:
foreach (var s in found)
{
Console.WriteLine(s);
} Others:
Chad talked about other thinks like OBA (Office Business Applications), WPF. The most important thing is that WPF works fine with Winforms. Winforms can host WPF components.
A very interesting presentation that Chad has shown for us was the History of Microsoft Office Download it and enjoy !!
Besides being funny, it shows how MS Office navigation had to evolve.
Chad just scratched the surface, but left us hungry for more knowledge about the existing new features.
