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+Rosetta example: Polymorphic copy
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+Let a polymorphic object contain an instance of some specific type S +derived from a type T. The type T is known. The type S is possibly +unknown until run time. The objective is to create an exact copy of +such polymorphic object.
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package req nxnx::Object provides a method copy which creates a deep copy of any
+source object (hence, polymorphic in the sense of this task), i.e.,
+it contains all structural and behavioral features of the source and
+preserves its signature type.
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nx::Class create T { + :property -accessor public {label "T"} +} +nx::Class create S -superclasses T { + :property -accessor public {label "S"} +} + +set client [nx::Object new { + :public object method duplicate {src} { + # this is the polymorphic call site + return [$src copy] + } +}] + +set t [T new] +% $t label get +T +set s [S new] +% $s label get +S
Provide two copies, using copy underneath
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set t2 [$client duplicate $t] +set s2 [$client duplicate $s]
Are the copies truly independent objects (identities)? Yes …
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% expr {$t2 ne $t} +1 +% expr {$s2 ne $s} +1
Are the copies offsprings of the source types/classes? Yes …
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% $t info class +::T +% $t2 info class +::T + +% $s info class +::S +% $s2 info class +::S
Do the copies operate exactly like their source objects? Yes …
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% $t label get +T +% $t2 label get +T + +% $s label get +S +% $s2 label get +S