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| − | =Unfolding=
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| − | When class ''D'' inherits from class ''B'' there is one very critical question. What form (in respect to unfolding) of ''B'' is taken into account for the inheritance semantics. Without an argument I state that it should be its completely unfolded form.
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| − |
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| − | This said we can state that ''D'' inherits from the completely unfolded class ''B''. It remains to be specified in what order ''D'' is unfolded. We will try to construct a partial order.
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| − | We list all the possible unfoldings that occur in the standard:
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| − |
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| − | # 8.6.6 Definition: Unfolded Inheritance Part of a class
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| − | # 8.5.24 Definition: Unfolded form of a possibly multiple declaration
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| − | # 8.9.13 Definition: Unfolded feature list of an Only clause
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| − | # 8.9.14 Definition: Unfolded Only clause
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| − | # 8.9.24 Definition: Local unfolded form of an assertion
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| − | # 8.10.2 Definition: Unfolded form of an assertion
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| − | # 8.10.11 Definition: Relative unfolded form of a Precursor
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| − | # 8.10.13 Definition: Unfolded form of a Precursor
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| − | # 8.10.30 Definition: Unfolded redeclaration
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| − | # 8.17.9 Definition: Unfolded form of a multi-branch
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| − | # 8.17.10 Definition: Unfolded form of an interval
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| − | # 8.20.5 Definition: Unfolded Creators part of a class
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| − | # 8.20.14 Definition: Unfolded form of a creation instruction
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| − | ==Definition: Coupled name==
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| − |
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| − | ====Motivation====
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| − | There are several situations in which the ECMA standard uses unfolded forms as a vehicle to describe semantics. When this unfolded forms need names, like in Precursor, inline agents and not isolated features, hese names have an influence on the semantics of the system. An example:
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| − | {|border="0" cellpadding="2" cellspacing="0" align="center"
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| − | |-valign="top" -halign="center"
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| − | |<code>[eiffel, N]
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| − | class
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| − | B
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| − | feature
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| − | f
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| − | do
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| − | (agent do g := g + 1; print (g) end).call ([])
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| − | end
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| − | g: INTEGER
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| − | end
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| − | </code>
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| − | |
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| − | <code>[eiffel, N]
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| − | class
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| − | D
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| − | inherit
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| − | B
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| − | rename f as f1, g as g1, select f1, g1 end
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| − | B
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| − | rename f as f2, g as g2 end
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| − | end
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| − | </code>
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| − | |}
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| − |
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| − | It feels natural to unfold class ''B'' first and then inherit ''D'' from its unfolded form before ''D'' is unfolded:
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| − | {|border="0" cellpadding="2" cellspacing="0" align="center"
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| − | |-valign="top" -halign="center"
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| − | |<code>[eiffel, N]
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| − | class
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| − | B
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| − | feature
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| − | f
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| − | do
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| − | (agent fict_name).call ([])
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| − | end
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| − | g: INTEGER
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| − |
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| − | fict_name
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| − | do
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| − | g := g + 1; print (g)
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| − | end
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| − | end
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| − | </code>
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| − | |
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| − | <code>[eiffel, N]
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| − | class
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| − | D
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| − | inherit
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| − | B
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| − | rename f as f1, g as g1, select f1, g1 end
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| − | B
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| − | rename f as f2, g as g2 end
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| − | end
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| − | </code>
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| − | |}
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| − | The call-equivalent of the inline-agent (here named fict_name) has a call to ''g'' which has several
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| − | potential versions in ''D''. Hence this is not a valid system.
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| − | The same problem can occur with calls to ''Precursor''. The programmer cannot do anything about it since he has no knowledge of the fictitious name of the call-equivalent.
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| − | There should have been some coupling between the name ''f'' and the name of the call-equivalent of the inline-agent. The unfolded form of a renaming would then also rename all the coupled name (a precise definition follows). Our final example would become:
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| − |
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| − | {|border="0" cellpadding="2" cellspacing="0" align="center"
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| − | |-valign="top" -halign="center"
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| − | |<code>[eiffel, N]
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| − | class
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| − | B
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| − | feature
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| − | f
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| − | do
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| − | (agent fict_name).call ([])
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| − | end
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| − | g: INTEGER
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| − |
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| − | fict_name
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| − | do
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| − | g := g + 1; print (g)
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| − | end
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| − | end
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| − | </code>
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| − | |
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| − | <code>[eiffel, N]
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| − | class
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| − | D
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| − | inherit
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| − | B
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| − | rename f as f1, fict_name1, g as g1
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| − | redefine f1, fict_name1, g1
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| − | select f1, fict_name1, g1 end
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| − | B
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| − | rename f as f2, fict_name as fict_name2, g as g2
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| − | redefine f2, fict_name2, g2 end
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| − | feature
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| − | f1 do (agent fict_name1).call ([]) end
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| − | fict_name1 do g1 := g1 + 1; print (g1) end
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| − | g1: INTEGER
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| − |
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| − | f2 do (agent fict_name2).call ([]) end
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| − | fict_name2 do g2 := g2 + 1; print (g2) end
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| − | g2: INTEGER
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| − | end
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| − | </code>
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| − | |}
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| − |
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| − | The redefinitions of ''f1'', ''fict_name1'', ''g1'', ''f2'', ''fict_name2'' and ''g2'' come with the unfolded form of not isolated features.
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| − | Please note that the unfolded form of ''D'' needs to select ''fict_name1'' or ''fict_name2'' for the system to be valid. But this select has no semantic influence.
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| − |
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| − | ====Definition====
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| − |
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| − | A feature name n can be '''coupled''' to another feature name .
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| − |
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| − | ====Change on renaming====
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| − |
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| − | The unfolded form of a renaming introduces renamings to new fictitious names for all the names coupled to one of the renamed names.
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| − |
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| − | Informal:
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| − | *Example Let feature names fc1 and fc2 be coupled to name f and feature name gc be coupled to g. The following renaming:
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| − | rename f as f', g as g'
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| − |
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| − | Has the unfolded form:
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| − |
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| − | rename f as f', fc1 as fc1', fc2 as fc2', g as g', gc as gc'
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| − |
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| − | Whereas fc1', fc2' and gc' are new unique names.
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| − |
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| − | ====Change on select====
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| − |
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| − | The unfolded form of a select introduces selects of all names coupled to one the originally selected names.
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| − |
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| − | ==A complex example with precursor==
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| − | {|border="0" cellpadding="2" cellspacing="0" align="center"
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| − | |-valign="top" -halign="center"
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| − | |<code>[eiffel, N]
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| − | class
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| − | A
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| − | feature
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| − | a: INTEGER
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| − | f do a := a + 1 end
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| − | g do f end
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| − | </code>
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| − | |
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| − | <code>[eiffel, N]
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| − | class
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| − | B
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| − | inherit
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| − | A redefine g end
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| − | feature
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| − | g do Precursor end
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| − | end
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| − | </code>
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| − | |
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| − | <code>[eiffel, N]
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| − | class
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| − | D
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| − | inherit
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| − | B
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| − | rename a as a1, f as f1, g as g1
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| − | select a1, f1, g1 end
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| − | B
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| − | rename a as a2, f as f2, g as g2 end
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| − | feature
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| − | end
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| − | </code>
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| − | |}
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| − |
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| − | Unfolded forms of ''A'' and ''B'':
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| − |
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| − | {|border="0" cellpadding="2" cellspacing="0" align="center"
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| − | |-valign="top" -halign="center"
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| − | |<code>[eiffel, N]
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| − | class
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| − | A
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| − | feature
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| − | a: INTEGER
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| − | f do a := a + 1 end
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| − | g, gp do f end
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| − | </code>
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| − | |
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| − | <code>[eiffel, N]
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| − | class
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| − | B
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| − | inherit
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| − | A redefine g end
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| − | feature
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| − | g do gp end
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| − | end
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| − | </code>
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| − | |}
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| − |
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| − | Unfolded form of ''D'':
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| − | {|border="0" cellpadding="2" cellspacing="0" align="center"
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| − | |-valign="top" -halign="center"
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| − | |<code>[eiffel, N]
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| − | class
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| − | D
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| − | inherit
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| − | B
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| − | rename a as a1, f as f1, g as g1, gp as gp1
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| − | redefine f1, g1, gp1 end
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| − | select a1, f1, g1, gp1 end
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| − | B
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| − | rename a as a2, f as f2, g as g2, gp as gp2
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| − | redefine f2, g2, gp2 end
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| − | feature
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| − | f1 do a1 := a1 + 1 end
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| − | g1 do gp1 end
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| − | gp1 do f1 end
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| − |
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| − | f2 do a2 := a2 + 1 end
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| − | g2 do gp2 end
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| − | gp2 do f2 end
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| − | end
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| − | </code>
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| − | |}
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| − |
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| − | ==New Behaviour of renaming and select==
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| − | The unfolded form of a renaming is the renaming itself plus the unfolded forms of the renamings of all the coupled names.
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| | =Precursor= | | =Precursor= |
The current definition of the Precursor semantics in the ECMA standard (8.10.11)
The classes ROUTINE, PROCEDURE, FUNCTION and the new class PREDICATE do not nicely fit in to the Eiffel language. Reasons:
A Precondition of a feature r of a class S is valid if and only if every feature f appearing in every
Assertion_clause of its unfolded form u satisfies the following two conditions for every class C to
which r is available:
1 Iff appears as feature of a call in u or any of its subexpressions, f is available to C.
