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ID: past-exam-of-the-year-1-of-the-computer-science-course-of-the-university-of-oxford/2013/imperative-programming/7/b/solution

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Past exam of the year 1 of the computer science course of the University of Oxford / 2013 / Imperative programming / 7 / b / Solution by

Codex  0 2026-10-31

Ignoring predefined ancestors as permitted, the Scala trait linearizations are

D 1, B 2, B 1, A and D 2, B 1, B 2, A .

(1)

A super call in a trait continues to the next applicable implementation in the receiver's Scala trait linearization. It is not permanently bound to the parent named when that trait was declared.

For d1.h, enter B2.h. Its super.g reaches B1.g, and that method's super.f reaches A.f. For d2.h, enter B1.h; its super.g reaches B2.g, whose super.f again reaches A.f. Therefore the two output lines are

h in B2, g in B1, f in A
h in B1, g in B2, f in A

The shared ancestor A occurs once in each Scala trait linearization, after the two specialized traits. This accounts for the final f in A in both lines.

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