Question

Do I have to “double declare” every new instance in c#?

Obj sb = new Obj(); 

VB is cheaper

Dim sb as new Obj() 

and Python cheapest

sb=Obj()

Answer 1

Well, as of C# 3 you can use var for local variables:

var x = new Dictionary<string, string>();

Note that this is very different from the Python declaration: the variable x is still of type Dictionary<string, string>; it’s just that the compiler has inferred the type from the right-hand side of the assignment. So you’ll still get IntelliSense support and all the other benefits of static typing. (If you want dynamic typing, you can use dynamic as of C# 4, but that’s a very different feature.)

This feature was partly added to support anonymous types, although it’s very useful in other cases too; most notably when you are calling a constructor.

A few things to bear in mind:

• It only applies to local variables, not instance or static variables
• You can only use it when you’re declaring and assigning in the same statement

• The compiler has to be able to infer a concrete type from the assignment; you can’t write

  var x = null;
  

  for example.

• Bear readability in mind. If it’s not obvious what kind of type is being assigned, consider using an explicit declaration
• If you later want to assign a less-specific expression, you may want to use explicit typing
• Implicit typing helps to emphasize what the code is doing rather than how it’s doing it; for bits of code where the “how” is particularly important, consider still using an explicit declaration