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Advanced Material

Advanced Material. The following slides contain advanced material and are optional. Outline. CAT calls Generic conformance For more information, see http:// dev.eiffel.com/Comparison_of_catcall_solutions (Some of the information may be outdated…). CAT: Changed availability or type.

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Advanced Material

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  1. Advanced Material The following slides contain advanced material and are optional.

  2. Outline • CAT calls • Generic conformance • For more information, see • http://dev.eiffel.com/Comparison_of_catcall_solutions • (Some of the information may be outdated…)

  3. CAT: Changed availability or type • class PARENT • feature • f do end • g (a: ANY) do end • h: ANY • end • classCHILD • inherit • PARENT • redefineg • export{NONE} f end • feature • g (a: STRING) do a.to_upperend • h: STRING • end Restricting export status Covariant redefinition of argument and result type

  4. Problems with CAT • class APPLICATION • feature • make • local • p: PARENT • c: CHILD • do • create {CHILD} p • p.f • p.g (1) • end • end Exported to NONE Wrong argument type will lead to runtime exception

  5. Solution to CAT • Changed availability (restricting export status) • Not allowed anymore in ECMA Eiffel • Covariant result type • This is not a problem • Covariant argument type • Currently checked at run-time • Different solutions proposed, not yet decided on a particular strategy

  6. Generic conformance • classAPPLICATION • feature • make • local • any_list: LIST [ANY] • string_list: LIST [STRING] • integer_list: LIST [INTEGER] • do • string_list := any_list • string_list := integer_list • integer_list := any_list • integer_list := string_list • any_list := string_list • any_list := integer_list • end • end      

  7. Generic conformance vs. changed type • class LIST [G] • feature • put (a: G) do end • first: G • end • interface class LIST [ANY] • feature • put (a: ANY) • first: ANY • end • interface classLIST [STRING] • feature • put (a: STRING) • first: STRING • end LIST [STRING] conforms to LIST [ANY], thus the changed type in the argument and result are like a covariant redefinition.

  8. Problems with generic conformance • class APPLICATION • feature • make • local • any_list: LIST [ANY] • string_list: LIST [STRING] • do • create string_list.make • any_list := string_list • any_list.put (1) • string_list.first.to_upper • end • end Wrong element type

  9. Solutions to generic conformance • Novariant conformance • No conformance between generics of different type • Used by C# • Usage-site variance • Specify conformance for each generic derivation • Used by Java • Definition-site variance • Specify conformance for each generic class • Implemented by CLR

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