A Monotonic Superclass Linearization for Dylan. Kim Barrett . Bob Cassels [email protected]>. Paul Haahr. In computing, the C3 superclass linearization is an algorithm used primarily to obtain the order It was first published at the OOPSLA conference, in a paper entitled “A Monotonic Superclass Linearization for Dylan”. It was adapted to the. The C3 superclass linearization algorithm is more intuitive and allows for greater monotonicity of method orderings, a consistent superclass linearization.
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In computingsuperclass C3 superclass linearization is an algorithm used primarily to obtain the order in which methods should be inherited the “linearization” in the presence of multiple inheritanceand is often termed Method Resolution Order MRO. The name “C3” is not an initialism. It is also available as an alternative, non-default MRO in the core of Perl 5 starting with version 5.
C3 exists on CPAN. The C3 superclass linearization of a class is the sum of the class plus a unique merge of the linearizations of its parents and a list of the parents itself.
The list of parents as the last argument to the merge process preserves the local precedence order of direct parent classes. The merge of parents’ linearizations and parents list is done by selecting the first head of the lists which does not appear in the tail all elements of a list except the first of any of the lists.
Note, that a good head may appear as the first element in multiple lists at the same time, but it is forbidden to appear anywhere else. The selected element is removed from all the lists where it appears as a head and appended to the output list. The process of selecting and removing a good head to extend the output list is repeated until all remaining lists are exhausted.
C3 superclass linearization — Open Dylan
If at some point no good head can be selected, because the heads of all remaining lists appear in any one tail of the lists, then the merge is impossible to compute due to inconsistent orderings of dependencies in the inheritance hierarchy and no linearization of the original class exists. A naive divide and conquer approach to computing the linearization of a class may invoke the algorithm recursively to find the linearizations of parent classes for the merge-subroutine.
However, superflass will result in an infinitely looping recursion in the presence of a cyclic class hierarchy. To detect such a cycle and to break the infinite recursion and to reuse the results of previous computations as an optimizationthe recursive invocation should be shielded against re-entrance of a previous argument by means of a cache or memoization.
From Wikipedia, the free encyclopedia. The name C3 refers to the three important properties of the resulting linearization: This article may be confusing or unclear to readers. Please help us clarify the article. There might be a discussion about this on the talk page.
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