Why does ReSharper want to use 'var' for everything? [duplicate]

Question

I've just started using ReSharper with Visual Studio (after the many recommendations on SO). To try it out I opened up a recent ASP.NET MVC project. One of the first and most frequent things I've noticed it suggesting is to change most/all my explicit declarations to var instead. For example:

//From This:
MyObject foo = DB.MyObjects.SingleOrDefault(w => w.Id == 1);
//To This:
var foo = DB.MyObjects.SingleOrDefault(w => w.Id == 1);

and so on, even with simple types such as int, bool, etc.

Why is this being recommended? I don't come from a computer science or .NET background, having "fallen into" .NET development recently, so I'd really like to understand what's going on and whether it's of benefit or not.

Answer 1

What ReSharper suggests is clearly overuse of the var keyword. You can use it where the type is obvious:

var obj = new SomeObject();

If the type is not obvious, you should rather write it out:

SomeObject obj = DB.SomeClass.GetObject(42);

Answer 2

One reason is improved readability. Which is better?

Dictionary<int, MyLongNamedObject> dictionary = new Dictionary<int, MyLongNamedObject>();

or

var dictionary = new Dictionary<int, MyLongNamedObject>();