C#•5mo ago

Create dynamic class that implements interface with static properties

Sorry for the PowerShell but I'm trying to figure out how to create a class that implements an interface with a static property and I have the following

using namespace System.Reflection
using namespace System.Reflection.Emit

$ErrorActionPreference = 'Stop'

Add-Type -TypeDefinition @'
public interface IProperty
{
    static abstract int Id { get; }
}

public class CSharpProperty : IProperty
{
    public static int Id { get => 1; }
}
'@

$ab = [AssemblyBuilder]::DefineDynamicAssembly(
    [AssemblyName]::new("MyAssembly"),
    [AssemblyBuilderAccess]::Run)
$mb = $ab.DefineDynamicModule("MyModule")
$tb = $mb.DefineType(
    "MyClass",
    [TypeAttributes]::Public,
    $null,
    [type[]]@([IProperty]))

$getAttr = $tb.DefineMethod(
    "get_Id",
    [MethodAttributes]"Public, Static, HideBySig, SpecialName",
    [int],
    [type]::EmptyTypes)
$getAttrIl = $getAttr.GetILGenerator()
$getAttrIl.Emit([OpCodes]::Ldc_I4_1)
$getAttrIL.Emit([OpCodes]::Ret)

$pb = $tb.DefineProperty(
    "Id",
    [PropertyAttributes]::None,
    [int],
    $null)
$pb.SetGetMethod($getAttr)

$null = $tb.CreateType()

[MyClass]::Id

using namespace System.Reflection
using namespace System.Reflection.Emit

$ErrorActionPreference = 'Stop'

Add-Type -TypeDefinition @'
public interface IProperty
{
    static abstract int Id { get; }
}

public class CSharpProperty : IProperty
{
    public static int Id { get => 1; }
}
'@

$ab = [AssemblyBuilder]::DefineDynamicAssembly(
    [AssemblyName]::new("MyAssembly"),
    [AssemblyBuilderAccess]::Run)
$mb = $ab.DefineDynamicModule("MyModule")
$tb = $mb.DefineType(
    "MyClass",
    [TypeAttributes]::Public,
    $null,
    [type[]]@([IProperty]))

$getAttr = $tb.DefineMethod(
    "get_Id",
    [MethodAttributes]"Public, Static, HideBySig, SpecialName",
    [int],
    [type]::EmptyTypes)
$getAttrIl = $getAttr.GetILGenerator()
$getAttrIl.Emit([OpCodes]::Ldc_I4_1)
$getAttrIL.Emit([OpCodes]::Ret)

$pb = $tb.DefineProperty(
    "Id",
    [PropertyAttributes]::None,
    [int],
    $null)
$pb.SetGetMethod($getAttr)

$null = $tb.CreateType()

[MyClass]::Id

It's failing with

Exception calling "CreateType" with "0" argument(s): "Virtual static method 'get_Id' is not implemented on type 'MyClass' from assembly 'MyAssembly, Version=0.0.0.0,Culture=neutral, PublicKeyToken=null'."

Looking at the IL code in sharplab.io for the equivalent C# code doesn't have anything jumping out at me https://sharplab.io/#v2:C4LglgNgPgAgzAAjAO2AUwE4DMCGBjNBASQAUMB7AB02AE8BYAKAG8mF2EYBGANgRwBGAZ2AZ8wJKmIATBMwQBzNMADcCAL5NNjJvE4AmBAGEAygAscGSmSo1aCEMRvUMdJq0YdOibnxQSiWXklCQBeAD4ELjVtdSA==. When adding the MethodAttributes.Virtual to the get_Id method builder it fails saying methods can't be static and virtual. Am I just missing something simple or is there something else I need to do here?

SharpLab

C#/VB/F# compiler playground.

11 Replies

Jimmacle•5mo ago

there a reason you chose this particular method of masochism? i've never seen someone try to dynamically generate C# from powershell

jborean•5mo ago

It's how PowerShell defines classes internally and for me to add support for this in normal pwsh classes in the PowerShell engine I need to know how to do it I was missing the following

$tb.DefineMethodOverride($getAttr, [IProperty].GetMethod("get_Id"))

$tb.DefineMethodOverride($getAttr, [IProperty].GetMethod("get_Id"))

Yawnder•5mo ago

There might be something about that in C# 11, but before that, you sure can't mix inheritance with static. It means that having both virtual and static on the same member can't be right.

jborean•5mo ago

Isn't that what an abstract static method/property on interfaces can do, it ensure you set that on the implementing type?

Yawnder•5mo ago

If you're in C#11 you could, but are you?

jborean•5mo ago

Yes

Unknown User•5mo ago

Message Not Public

jborean•5mo ago

I don’t control how pwsh does things, I just need to fix it and this was asking how to do thing in the way that pwsh works. Ultimately it was DefineMethodOverride that was needed

Jimmacle•5mo ago

i would assume a lot of assemblies powershell uses are written in some .NET language and not actually in powershell but i'm not a powershell user so idk

jborean•5mo ago

This is part of powershell itself not a powershell module

jborean•5mo ago

It supports defining classes through a PowerShell syntax at runtime https://learn.microsoft.com/en-us/powershell/module/microsoft.powershell.core/about/about_classes?view=powershell-7.4 and uses TypeBuilder to do so. It just doesn’t currently support implementing an interface with a static abstract/virtual member hence me trying to figure out how to do so using TypeBuilder

about Classes - PowerShell

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Create dynamic class that implements interface with static properties