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

Question

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,

Answer 1

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:

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

  • 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.

    • See the following GitHub issues:
      • #3461 (using module) and #2074 (using assembly)
      • #6652 - a meta issue tracking all class-related issues.

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

• Note: The ScriptsToProcess entry would work too, but the scripts it references are dot-sourced in (loaded into the current scope of) the caller, not the enclosing module.
  With types from compiled code (including ad hoc-compiled code with Add-Type), that works too, because such types invariably become available session-globally, but it is conceptually cleaner to use NestedModules, because it dot-sources scripts in the enclosing module's scope