VB.NET equivalent to C# var keyword

Question

Is there a VB.NET equivalent to the C# var keyword?

I would like to use it to retrieve the result of a LINQ query.

Answer 1

Omitting the type in VB.NET (VB9) will implicitly type the variable.

This is not the same as "option strict off" in previous versions of VB.NET, as the variable is strongly-typed, it's just done so implicitly (like the C# var) keyword.

Dim foo = "foo"

foo is declared as a String.

Option Infer must be on in order for this to function properly

Answer 2

Simply use the conventional Dim keyword without a type.

But beware that you need to enable both Option Strict and Option Infer to make this work, otherwise the code either will not compile (Strict On, Infer Off) or will declare the variable as of type Object, which isn’t what you want (Strict Off).

Minimal working example:

Option Strict On
Option Infer On

Imports System

Module MainModule
    Sub Main()
        Dim i = 42
        Dim s = "Hello"
        Console.WriteLine("{0}, {1}", i.GetType(), s.GetType())
        ' Prints System.Int32, System.String '
    End Sub
End Module

Answer 3

You need Option Infer On and then just use the Dim keyword, thus:

Dim query = From x In y Where x.z = w Select x

Contrary to some of the other answers, you do not need Option Strict On.

If you're using the VS IDE you can just hover over the variable names, but to get the compile-time types of variables (GetType(variableName) does not compile - "Type '<variablename>' is not defined." - and VarType(variable) is actually just the VB version of variable.GetType() which returns the type of the instance stored in the variable at runtime) I used

Function MyVarType(Of T)(ByRef Var As T) As Type
    Return GetType(T)
End Function

In detail:

• without Dim:

  Explicit Off, gives Object

  Explicit On, error "Name '' is not declared."

• with Dim:

  • Infer On, gives expected types

  • Infer Off:

    Strict On, error "Option Strict On requires all declarations to have an 'As' clasue."

    Strict Off, gives Object