Sharing “var” across the method
One of the biggest limitation in “var” is that it cannot be shared across the methods. So if you are doing something using that keyword then you have to stick to the local. I was reading Alex’s Blog where he explained it very nicely,
Here is my implementation,
Create an Extension method
static class MyClass
{
//Create Extension Method to covert the var
public static T CastVar<T>(this object obj, T anyType)
{
return (T)obj;
}
}
Now suppose you want to get output of type “var” from any method,
public static object GetVAR()
{
var list = new List<int> { 1, 2, 3, 4, 5, 6, 7, 8, 9 };
return (object)list;
}
Retrieve it to an object.
object o = GetVAR();
Next is the tricky part, as per Alex
“ This works because when an anonymous type is used the compiler first checks that one with the same signature (i.e. all fields are the same name and type) hasn't already been used. If one has the same CLR type is used.”
You need to know the shape of the object to put it again back to “var” type.
var o1 = o.CastVar(new List<int>{1});
Now this iteration will work perfectly fine as if you are working with any other local “var”.
foreach (int i in o1)
{
Console.WriteLine(i);
}
I have tested this for LINQ to SQL where we use “var” very frequently,
static void Main(string[] args)
{
object o = GetVAR();
var query = o.CastVar(new[] {new {CID = "", Company = ""}});
foreach (var c in query)
{
Console.WriteLine("{0} - {1}", c.CID, c.Company);
}
}
public static object GetVAR()
{
NWDataContext db = new NWDataContext();
var q = from c in db.Customers
where c.City == "London"
select new
{
CID = c.CustomerID,
Company = c.CompanyName
};
return (object)q.ToArray();
}
Namoskar!!!
Comments
Anonymous
December 18, 2007
One of the biggest limitation in “var” is that it cannot be shared across the methods. So if you areAnonymous
January 04, 2008
HELLO THIS IS VERY NICE ARTICALAnonymous
January 18, 2008
This Looks good way of transferring var types...but Is there any Problem associated with it..or Performance issues (in case of large queries )since u r casting it to object then back to original var type..?? It is interesting way to achieve it...Anonymous
April 28, 2009
I think you're confusing the var keyword with Anonymous Types. There is some overlap, but they are not the same thing. For instance: var someProductObject = new Product(); someProductObject is of type Product - var in this case is just a shortcut in declaring the variable. The compile still treats this as a statically typed object and this can be passed to just like any other variable. var someAnonymousType = new {Id=1, Name="Kelly"}; This is an anonymous type. The compiler will generate a type definition for this at compile time, but because it's a compile time created type, you can't pass these to other methods and have those methods understand they're type.Anonymous
August 07, 2009
Thank you so much. I really enjoyed.