Visual Basic .NET Language Option Infer When to use type inference
Example
Basically you can use type inference whenever it is possible.
However, be careful when combining Option Infer Off and Option Strict Off, as this can lead to undesired run-time behavior:
Dim someVar = 5
someVar.GetType.ToString() '--> System.Int32
someVar = "abc"
someVar.GetType.ToString() '--> System.String
Anonymous Type
Anonymous types can only be declared with Option Infer On.
They are often used when dealing with LINQ:
Dim countryCodes = New List(Of String)
countryCodes.Add("en-US")
countryCodes.Add("en-GB")
countryCodes.Add("de-DE")
countryCodes.Add("de-AT")
Dim q = From code In countryCodes
Let split = code.Split("-"c)
Select New With {.Language = split(0), .Country = split(1)}
-
Option Infer On
The compiler will recognize the anonymous type:
-
Option Infer Off
The compiler will either throw an error (withOption Strict On)
or will considerqas typeobject(withOption Strict Off).
Both cases will produce the outcome that you cannot use the anonymous type.
Doubles/Decimals
Numeric variables with decimal places will be infered as Double by default:
Dim aNumber = 44.11 '--> Will be treated as type `Double` by the compiler
If another type like Decimal is desired the value which initialized the variable needs to be marked:
Dim mDecimal = 47.11D '--> Will be treated as type `Decimal` by the compiler
