Talk:New CAT call - Revision history

Juliant at 09:15, 24 February 2007

2007-02-24T09:15:34Z

Juliant at 08:47, 24 February 2007

2007-02-24T08:47:11Z

Juliant at 08:46, 24 February 2007

2007-02-24T08:46:06Z

Manus at 21:23, 22 February 2007

2007-02-22T21:23:05Z

Nenieorg at 13:22, 22 February 2007

2007-02-22T13:22:29Z

Nenieorg at 13:20, 22 February 2007

2007-02-22T13:20:58Z

Schoelle at 08:56, 15 November 2006

2006-11-15T08:56:40Z

Schoelle at 08:55, 15 November 2006

2006-11-15T08:55:41Z

Schoelle at 08:45, 15 November 2006

2006-11-15T08:45:01Z

Manus: Fixed my original comment and responded to latest one.

2006-11-09T18:24:09Z

Fixed my original comment and responded to latest one.

@@ Line 15: / Line 15: @@
 '''--[[User:Juliant|Juliant]] 09:46, 24 February 2007 (CET)'''
-I would say <e>? STRING</e> means <e>STRING</e> or <e>Void</e>. ECMA talks about certified attachment patterns, chapter 8.24.10. Item 2 about the read-only entity says that you can use a detached type after a read-only void test:
+I would say <e>? STRING</e> means <e>STRING</e> or <e>Void</e>. ECMA talks about certified attachment patterns (chapter 8.24.10). Item 2 about the read-only entity says that you can use a detached type after a read-only void test:
 <e>
 local
@@ Line 25: / Line 25: @@
 end
 </e>
-So you cannot assign anything else than a <e>STRING</e> to a detached type <e>? STRING</e>, even after a cat-call in a covariantly redefined features. So after a cat-call you need to pass Void to the feature and not a wrongly attached type, or the void test needs to test types as well (which would make it equivalent to the object test).
+If you would be able to assign anything else than a <e>STRING</e> to a detached type <e>? STRING</e> then the void test would need to test types as well (which would make it equivalent to the object test).

@@ Line 25: / Line 25: @@
 end
 </e>
-So you cannot assign anything else than a <e>STRING</e> to a detached type <e>? STRING</e>, even after a cat-call in a covariantly redefined features. So after a cat-call you need to pass Void to the feature and not a wrongly attached type.
+So you cannot assign anything else than a <e>STRING</e> to a detached type <e>? STRING</e>, even after a cat-call in a covariantly redefined features. So after a cat-call you need to pass Void to the feature and not a wrongly attached type, or the void test needs to test types as well (which would make it equivalent to the object test).

← Older revision		Revision as of 08:46, 24 February 2007
Line 12:		Line 12:

	:'''--[[User:Manus\|manus]] 22:23, 22 February 2007 (CET)''' It is not allowed but depending on the semantics you give to the reattachment in the case of a catcall, it is as if you have contravariance. But currently although the standard is not clear on the subject, it is better to say it is Void rather than attached to the wrong type.		:'''--[[User:Manus\|manus]] 22:23, 22 February 2007 (CET)''' It is not allowed but depending on the semantics you give to the reattachment in the case of a catcall, it is as if you have contravariance. But currently although the standard is not clear on the subject, it is better to say it is Void rather than attached to the wrong type.
		+
		+	'''--[[User:Juliant\|Juliant]] 09:46, 24 February 2007 (CET)'''
		+
		+	I would say <e>? STRING</e> means <e>STRING</e> or <e>Void</e>. ECMA talks about certified attachment patterns, chapter 8.24.10. Item 2 about the read-only entity says that you can use a detached type after a read-only void test:
		+	<e>
		+	local
		+	e: ? STRING
		+	do
		+	if e /= Void then
		+	e.to_lower
		+	end
		+	end
		+	</e>
		+	So you cannot assign anything else than a <e>STRING</e> to a detached type <e>? STRING</e>, even after a cat-call in a covariantly redefined features. So after a cat-call you need to pass Void to the feature and not a wrongly attached type.

← Older revision		Revision as of 21:23, 22 February 2007
Line 10:		Line 10:

	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)		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)
		+
		+	:'''--[[User:Manus\|manus]] 22:23, 22 February 2007 (CET)''' It is not allowed but depending on the semantics you give to the reattachment in the case of a catcall, it is as if you have contravariance. But currently although the standard is not clear on the subject, it is better to say it is Void rather than attached to the wrong type.

← Older revision		Revision as of 13:22, 22 February 2007
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−	''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]]	+	''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 covariance, changing STRING into ANY is contravariance--[[User:Manus\|manus]] 18:38, 8 November 2006 (CET)

← Older revision		Revision as of 13:20, 22 February 2007
Line 8:		Line 8:

	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)		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)

← Older revision		Revision as of 08:56, 15 November 2006
Line 7:		Line 7:
	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)		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. --[[User:Schoelle\|Schoelle]] 09:45, 15 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)

← Older revision		Revision as of 08:55, 15 November 2006
Line 7:		Line 7:
	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)		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. --[[User:Schoelle\|Schoelle]] 09:45, 15 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. --[[User:Schoelle\|Schoelle]] 09:45, 15 November 2006 (CET)

← Older revision		Revision as of 08:45, 15 November 2006
Line 6:		Line 6:

	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)		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. --[[User:Schoelle\|Schoelle]] 09:45, 15 November 2006 (CET)

@@ Line 1: / Line 1: @@
 ''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 covariance--[[User:Manus|manus]] 18:38, 8 November 2006 (CET)
+Changing ANY into STRING is covariance, changing  STRING into ANY is contravariance--[[User:Manus|manus]] 18:38, 8 November 2006 (CET)
-Hmm - that sentence does not make sense. I assume you wanted to say ''STRING into ANY is contravariance''. But that was not the point. 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 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)