{"id":69,"date":"2012-06-26T05:27:11","date_gmt":"2012-06-26T03:27:11","guid":{"rendered":"https:\/\/nikostotz.de\/blog\/?p=69"},"modified":"2012-06-26T05:52:44","modified_gmt":"2012-06-26T03:52:44","slug":"parallel-type-trees-generic-attribute-vs-generic-accessor-method","status":"publish","type":"post","link":"https:\/\/www.nikostotz.de\/blog\/parallel-type-trees-generic-attribute-vs-generic-accessor-method\/","title":{"rendered":"Parallel Type Trees: Generic Attribute vs. Generic Accessor Method"},"content":{"rendered":"

\nWhen working with ecore<\/a> models, we often encounter super\/subtype relations on both the container and the member side. We want to easily access both the generic<\/em> and the specific<\/em> container members. Intuitively, we used different approaches to fulfill this requirement. This article explores some implementation possibilities and examines their advantages, drawbacks and performance implications.\n<\/p>\n

Scenario<\/h2>\n

\nAs example, we’ll use an AbstractLibrary<\/span><\/code> containing many AbstractEntry<\/span><\/code>s. We have a specialized BookLibrary<\/span><\/code> containing Book<\/span><\/code>s and a specialized MovieLibrary<\/span><\/code> containing Movie<\/span><\/code>s and its subtypes SciFi<\/span><\/code>s and Comedy<\/span><\/code>s. Both AbstractLibrary<\/span><\/code> and AbstractEntry<\/span><\/code> are considered generic<\/em>, while all other types are considered specific<\/em>.\n<\/p>\n

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Situation<\/h2>\n

\nTypical tasks when working with models include verification and generation. We might want to assure every library has at least some content, or generate an XML descriptor for any entry in any library. In both cases, we’re not interested in the specific type of library or entry. At the same time, we might want to check all books to have an author, or generate different descriptors for science fiction movies and comedies.\n<\/p>\n

\nTherefore, we would need a list of generic entries in any library, and specific typed lists it specific libraries. Unfortunately, ecore prohibits overriding attributes. This limitation is not that important for single references, as we can easily define getter\/setter to cast the return\/parameter type as required. It gets much more complicated on multi-valued references.\n<\/p>\n

Requirements<\/h2>\n

\nOn multi-valued references (aka lists), we want to<\/p>\n