Load an dll class library with autolisp

This tutorial aims to guide for load a dll file with autolisp code
The file dll name, in this sample, is 'Mydll.dll' with class name 'class1' (Register your dll file for lisp application)
In this case the dll file contains a sample function 'Public Function s_con(ByVal s_first As String, ByVal s_second As String )' (vb.net code)
The sample function 's_con' return a concatenation of first string variable and second string variable.
The autolisp code is:

Load dll with autolisp code

set value for string variable to pass dll function (setq S_f_string "conca" S_f_string "tenate")
loads the extended AutoLISP functions Active X (vl-load-com)
get the main AutoCAD application object (setq acapp (vlax-get-acad-object))
load VB ActiveX DLL into AutoCAD's address space (setq class (vla-GetInterfaceObject acapp "Mydll.class1"))
Sample controll error line command (if (not class)
(princ "\nError loading MyClass.dll.\n")
(princ "\nMyClass.dll loaded.\n")
)
invoke and return value of dll function(setq out (vlax-invoke class 's_con S_f_string S_S_string))
print valueout

Complete function :

(function my_dll(/ class acapp)
    (setq S_f_string "conca"
    S_f_string "tenate"
    )
    (vl-load-com)
    (setq acapp (vlax-get-acad-object))
    (setq class (vla-GetInterfaceObject acapp "Mydll.class1"))
    (if (not class)
     (princ "\nMyClass.dll loaded.\n")
     (princ "\nError loading MyClass.dll.\n")
   )
   (setq out (vlax-invoke class 's_con S_f_string S_S_string))
   out
)

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