VB.Net Generics Constraints Equivalent to C# where TValue : New()

Question

I am working on converting an extension method I have in C# into VB.Net, but can't figure out the correct way to set a constraint on the output.

My current C# code is working on a Dictionary and looks as follows:

public static TValue GetOrCreate<TKey, TValue>(this IDictionary<TKey, TValue> dict, TKey key)
    where TValue : new()
{   }

I've seen questions explaining how to set the constraint on the inputs such as here, but I can't seem to find one explaining how to convert the output constraint of where TValue : new()

I'm sure it's easy, but I've grown a bit rusty with VB and hoping someone here knows it off the top of their head.

[VB.Net Generic Procedures](https://learn.microsoft.com/en-us/dotnet/visual-basic/programming-guide/language-features/data-types/generic-procedures) - the constraints go directly inside the `(Of ...)` between procedure name and argument list. See the example `Public Function findElement(Of T As IComparable)` — Damien_The_Unbeliever, Feb 11 '20 at 16:56
The syntax is actually the same for inputs and outputs, see https://stackoverflow.com/a/25256115/1968 — Konrad Rudolph, Feb 11 '20 at 16:57
Does this answer your question? [Any VBNET equivalence of C# where generic constraint keyword?](https://stackoverflow.com/questions/2803933/any-vbnet-equivalence-of-c-sharp-where-generic-constraint-keyword) — madreflection, Feb 11 '20 at 16:57

score 5 · Accepted Answer · edited Feb 11 '20 at 21:08

5

Here's the conversion, as obtained from Telerik's Code Converter:

Module Extensions
  <Extension()>
  Public Function GetOrCreate(Of TKey, TValue As New)(ByVal dict As IDictionary(Of TKey, TValue), ByVal key As TKey) As TValue

  End Function
End Module

edited Feb 11 '20 at 21:08

djv

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answered Feb 11 '20 at 16:57

InteXX

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Beat me to it by about 30 seconds. – Joel Coehoorn Feb 11 '20 at 16:59
WOOHOO!!! - The trick was the `GetOrCreate(Of TKey, TValue As New)` - Thank you!!! – John Bustos Feb 11 '20 at 17:01
I saw people's comments, but none of them made sense / worked - THIS gave me the answer. Thank you!! – John Bustos Feb 11 '20 at 17:02
Also: there was an edit to remove the `Shared` modifier, which I rolled back. `Shared` should be removed if the method is part of a Module, but is still needed if the method is part of Class. Since this code is being converted from C#, I believe the latter is more likely. – Joel Coehoorn Feb 11 '20 at 17:02
@AhmedAbdelhameed Was already typing a response separately, just took a minute to have it ready. – Joel Coehoorn Feb 11 '20 at 17:03
@JoelCoehoorn Correct me if I'm wrong but a VB extension method _**Must**_ be defined in a module as I mentioned in the edit message. – 41686d6564 stands w. Palestine Feb 11 '20 at 17:03
@AhmedAbdelhameed Generally that is true, but IIRC there are ways around it. But maybe those required reflection games or similar. It's been a while. – Joel Coehoorn Feb 11 '20 at 17:04
@JoelCoehoorn ~ To clarify the `Shared` situation, I edited the code a bit. – InteXX Feb 11 '20 at 17:21
@JohnBustos ~ YW :-) – InteXX Feb 11 '20 at 17:22
@AhmedAbdelhameed ~ `... a VB extension method Must be defined in a module ...` Yes, that's correct. In my experience, at least. I've not experimented with putting one in a class as Joel suggests might be possible. In any event, I haven't run across a situation that would make it worth the extra trouble. Modules are easy. So easy, in fact, that I created three of them yesterday ;-) – InteXX Feb 11 '20 at 18:40

VB.Net Generics Constraints Equivalent to C# where TValue : New()

1 Answers1