This is a coding exercise I am currently working on to get myself familiarized with COM.

Example IDL comparsion

https://www.codeproject.com/Articles/8679/Building-a-LOCAL-COM-Server-and-Client-A-Step-by-S

https://adapt-and-attack.com/2020/05/12/building-a-com-server-for-initial-execution/

import "oaidl.idl";

// define IStats interface
[object, uuid(FE78387F-D150-4089-832C-BBF02402C872),
 oleautomation, helpstring("Get the status information about this car")]
interface IStats : IUnknown
{
   HRESULT DisplayStats();
   HRESULT GetPetName([out,retval] BSTR* petName);
};

// define the IEngine interface
[object, uuid(E27972D8-717F-4516-A82D-B688DC70170C),
 oleautomation, helpstring("Rev your car and slow it down")]
interface IEngine : IUnknown
{
   HRESULT SpeedUp();
   HRESULT GetMaxSpeed([out,retval] int* maxSpeed);
   HRESULT GetCurSpeed([out,retval] int* curSpeed);
};

// define the ICreateMyCar interface
[object, uuid(5DD52389-B1A4-4fe7-B131-0F8EF73DD175),
 oleautomation, helpstring("This lets you create a car object")]
interface ICreateMyCar : IUnknown
{
   HRESULT SetPetName([in]BSTR petName);
   HRESULT SetMaxSpeed([in] int maxSp);
};

// library statement
[uuid(957BF83F-EE5A-42eb-8CE5-6267011F0EF9), version(1.0),
 helpstring("Car server with typeLib")]
library CarLocalServerLib
{
   importlib("stdole32.tlb");
   [uuid(1D66CBA8-CCE2-4439-8596-82B47AA44E43)]
   coclass MyCar
   {
      [default] interface ICreateMyCar;
      interface IStats;
      interface IEngine;
   };
};

// Interface
[
	object,
	uuid(44568f24-d895-42a4-97ee-db91c60cc1c4),
	helpstring("Leos Test Class"),
	pointer_default(unique),
	dual,
	oleautomation
]
interface ITestClass : IDispatch
{
	import "oaidl.idl";
	HRESULT SetData([in] BSTR data);
	HRESULT Run();
};

// Type Library
[
	uuid("44568f25-d895-42a4-97ee-db91c60cc1c4"),
	version(1.0),
	helpstring("TestClass Type Library")
]
library TestClassLib
{
	importlib("stdole32.tlb");
	
	[
		uuid("44568f26-d895-42a4-97ee-db91c60cc1c4"),
		helpstring("TestClass Component Class")
	]
	coclass TestClass
	{
		[default] interface ITestClass;
	};
};

Different default interfaces def

		//IUnknown		
		ULONG __stdcall AddRef();
    ULONG __stdcall Release();
    HRESULT __stdcall QueryInterface(REFIID riid, void** ppv);
    // IDispatch
		HRESULT __stdcall GetTypeInfoCount(UINT* pctinfo);
    HRESULT __stdcall GetTypeInfo(UINT iTypeInfo, LCID, ITypeInfo** ppTypeInfo);
		HRESULT __stdcall GetIDsOfNames(REFIID riid, LPOLESTR* rgszNames, UINT cNames, LCID, DISPID* rgDispId);
    HRESULT __stdcall Invoke(DISPID dispIdMember, REFIID riid, LCID, WORD wFlags, DISPPARAMS* pDispParams, VARIANT* pVarResult, EXCEPINFO* pExcepInfo, UINT* puArgErr);
    // ITestClass
    HRESULT __stdcall SetData(wchar_t* data);
    HRESULT __stdcall Run();

Data Types in Interface Body

https://learn.microsoft.com/en-us/windows/win32/midl/data-types-in-the-interface-body