EiffelStudio: an EiffelSoftware project - User contributions [en]

Talk:New CAT call

2007-02-22T13:22:29Z

Nenieorg:

''The most obvious observation is, that this weakens the new non-void typing mechanism, it is now possible to pass Void to feature f of class B2. This was probably not the intention of the programmer.'' - I do not understand this comment. Changing a:ANY into a:?STRING looks like a standard contravariant redefinition to me. Such redefinitions are sound. --[[User:schoelle]]

Changing ANY into STRING is covariance, changing STRING into ANY is contravariance--[[User:Manus|manus]] 18:38, 8 November 2006 (CET)

Changing ANY into ?STRING is contravariant. ''Could be STRING'' is more permissive than ''must be ANY'' as the first can contain any value, while the second may not contain Void. --[[User:Schoelle|Schoelle]] 10:01, 9 November 2006 (CET)

Changing ANY into ?STRING is not contravariance, it is covariance. Seeing it contravariant is possible a side effect of one of the interpretation of the current standard when looking at the semantic. I think we need another terminology here to describe this unspecified semantics.--[[User:Manus|manus]] 19:24, 9 November 2006 (CET)

Sorry, but I have to object: ANY into ?STRING '''is contravariant''': Any value of type ANY is a valid value of type ?STRING. AFAIK this is what contravariant means. I do not see any reason why we should invent a new name. Actually, all non-attached types are completely equivalent: they all can take any value. The type is only a hint for the create call and a comment. --[[User:Schoelle|Schoelle]] 09:45, 15 November 2006 (CET)

Do you mean ''local s: ?STRING; a: ANIMAL do s := a end'' is allowed (in general as opposed to the context of covariant redefinition)? I thought the semantic of ?X was "X or Void" that is basically the same as X in classic Eiffel. If we don't have a type to mean "X or Void" it seems like a severe flaw of the Void-checking side of things. --[[User:Nenieorg|Nenieorg]] 14:20, 22 February 2007 (CET)

Talk:New CAT call

2007-02-22T13:20:58Z

Nenieorg:

''The most obvious observation is, that this weakens the new non-void typing mechanism, it is now possible to pass Void to feature f of class B2. This was probably not the intention of the programmer.'' - I do not understand this comment. Changing a:ANY into a:?STRING looks like a standard contravariant redefinition to me. Such redefinitions are sound. [[User:schoelle]]

Changing ANY into STRING is covariance, changing STRING into ANY is contravariance--[[User:Manus|manus]] 18:38, 8 November 2006 (CET)

Changing ANY into ?STRING is contravariant. ''Could be STRING'' is more permissive than ''must be ANY'' as the first can contain any value, while the second may not contain Void. --[[User:Schoelle|Schoelle]] 10:01, 9 November 2006 (CET)

Changing ANY into ?STRING is not contravariance, it is covariance. Seeing it contravariant is possible a side effect of one of the interpretation of the current standard when looking at the semantic. I think we need another terminology here to describe this unspecified semantics.--[[User:Manus|manus]] 19:24, 9 November 2006 (CET)

Sorry, but I have to object: ANY into ?STRING '''is contravariant''': Any value of type ANY is a valid value of type ?STRING. AFAIK this is what contravariant means. I do not see any reason why we should invent a new name. Actually, all non-attached types are completely equivalent: they all can take any value. The type is only a hint for the create call and a comment. --[[User:Schoelle|Schoelle]] 09:45, 15 November 2006 (CET)

Do you mean ''local s: ?STRING; a: ANIMAL do s := a end'' is allowed (in general as opposed to the context of covariant redefinition)? I thought the semantic of ?X was "X or Void" that is basically the same as X in classic Eiffel. If we don't have a type to mean "X or Void" it seems like a severe flaw of the Void-checking side of things. --[[User:Nenieorg|Nenieorg]] 14:20, 22 February 2007 (CET)