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How to use interfaces in Powershell defined via Add-Type?

I developed a PowerShell module that relied on a .NET Assembly for some operations.

I refactored this module to not need that Assembly and noticed some strange behavior, which blocks me from removing the class at last:

Add-Type -TypeDefinition "public interface ICanTalk string talk(); " -Language CSharp

class Talker : ICanTalk
[string] talk() return "Well hello there";



If you run this commands interactively, it will succeed.
But as soon as I run it "en-bloque" in ISE or from a psm1 file, it will throw an error, stating it cannot find the interface defined in the Add-Type call.

Add-Type

I can reproduce the problem in both Windows-PowerShell and PowerShell Core (6.0.2)

What is the reason for the different behaviour and how can I tackle it?

Add-Type

2 Answers
2

Apparently PowerShell will read the file and handle class-definitions before executing the code.

To solve this problem, the Add-Type needs to be put into an own script file, which is run before the module loads (or in ISE, just run the code before running the class definitions).

Add-Type

This can be accomplished by using ScriptsToProcess from the PSD1 file.

Kudos to @TheIncorrigible1 for putting me on the track.

To complement your own answer:

PowerShell class and enum definitions are parsed before execution begins and any types referenced in such definitions must either be:

class

enum

loaded into the current the session beforehand.

[only partially implemented as of Windows PowerShell v5.1 / PowerShell Core 6.1.0]
loaded via a using module / using assembly statement at the very
top of the file.

using module

using assembly

using module already works, but only if the referenced types are themselves class / enum definitions.

using module

class

enum

Currently, types loaded from assemblies - whether via a module containing assemblies imported with using module or using assembly to directly load an assembly - aren't yet detected.

using module

using assembly

using module

using assembly

The workaround in the meantime is to load the referenced types via a separate script beforehand, by using the module manifest's NestedModules entry.

NestedModules

ScriptsToProcess

Add-Type

NestedModules

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