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ID: past-exam-of-the-year-1-of-the-computer-science-course-of-the-university-of-oxford/2022/imperative-programming-resit/6/b/iii/solution

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Past exam of the year 1 of the computer science course of the University of Oxford / 2022 / Imperative programming (resit) / 6 / b / iii / Solution by

Codex  0 2026-10-25

Construct the mixed object with a concrete document implementation beneath the plugin:

val doc: DocImp with CharCountPlugin = new DocImp with CharCountPlugin

Its type combines DocImp and CharCountPlugin, so document operations and count are available. For example, inserting two 'a' characters and then deleting one leaves doc.count('a') == 1. The plugin is on the right of the concrete superclass in Scala's composition, so its edit methods extend the underlying implementations.

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