Dynamically loading Object Icon code

Object Icon includes a small enhancement to MT Icon which allows procedures and classes to be loaded and invoked dynamically from other icode files (ie executable files created by the linker).

To illustrate how this works, consider the following simple source file:-

import io

invocable X, p

class X()
   public hello()
      write("Hello")
   end
end

procedure p()
   write("Hello again")
end

procedure main()
end

If this were in the file abc.icn, then it could be compiled with the command oit abc.icn. Then its symbols could be loaded and used dynamically as follows :-

import io, lang

procedure main()
   local prog, x
   prog := Prog.load("abc") | stop("Couldn't load")

   # Create an instance of X, call hello method
   x := Prog.get_global("X", prog)()
   x.hello()

   # Call procedure p
   Prog.get_global("p", prog)()
end

Some points to note.

• The “library” program needs a dummy main procedure. It also needs to declare the procedure and class as invocable, so that the linker doesn’t discard them as unreferenced symbols.
• The class could also be accessed via Class.for_name("X", prog)().
• The procedure could also be accessed via the call proc("p",,prog)()
• The loaded program retains its own separate set of global identifiers. References to global identifiers in loaded procedures and methods always refer to the enclosing loaded program. Hence, several global identifiers with the same name can co-exist at the same time in separate programs.