PR# 19413 [er] Full class checking and VGCC-2

When compiling the code below in full_class_checking mode, we get a VGCC-2 error:

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
VGCC(2)	Creation instruction applies to target of a deferred type.	

Type error: creation instruction applies to target of a deferred type.
What to do: make sure that type of target is effective.  

Class: DISPOSABLE_HASH_TABLE [G, H -> HASHABLE]
Source class: HASH_TABLE [G, K -> HASHABLE]
Feature: empty_duplicate
Creation of: Result
Target type set: [detachable like Current] detachable DISPOSABLE_HASH_TABLE [Generic #1, Generic #2]
Deferred classes: DISPOSABLE_HASH_TABLE 
Line: 1144
      do
->      create Result.make (n)
        if object_comparison then	
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~			

This is unfortunate because 'Result' is declared of type 'like Current' and the current class being deferred, there is no danger to create such thing at run-time.

To fix this error, one has to undefined feature `empty_duplicate' in the deferred class DISPOSABLE_HASH_TABLE and then copy/paste it back in all its concrete descendants. This is not attractive and error prone if in the implementation of `empty_duplicate' gets changed in class HASH_TABLE in the future.

In the Gobo tools, such error (creation of an entity of type 'like Current' when checked from a deferred descendant class) is not reported when checking the validity of features in the context of descendant classes in full class checking mode. It would be nice if EiffelStudio could do the same.

--
Eric Bezault

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
class TEST

create

	make

feature

	make
		local
			ht: MY_HASH_TABLE [STRING, STRING]
		do
			create ht.make (10)
		end

end
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
deferred class DISPOSABLE_HASH_TABLE [G, H -> detachable HASHABLE]

inherit

	HASH_TABLE [G, H]
	
	DISPOSABLE
		undefine
			copy, is_equal
		end

end
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
class MY_HASH_TABLE [G, H -> detachable HASHABLE]

inherit

	DISPOSABLE_HASH_TABLE [G, H]

create

	make,
	make_equal

feature

	dispose
		do
		end

end
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

I just realized that copy/paste is not the only solution. We can just inherit again from HASH_TABLE in MY_HASH_TABLE to bring back the implementation of `empty_duplicate'.

--
Eric Bezault