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Dec 13, 2019
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Resync #8

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3 changes: 3 additions & 0 deletions acyclic-visitor/README.md
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Expand Up @@ -17,6 +17,7 @@ Allow new functions to be added to existing class hierarchies without affecting

## Applicability
This pattern can be used:

* When you need to add a new function to an existing hierarchy without the need to alter or affect that hierarchy.
* When there are functions that operate upon a hierarchy, but which do not belong in the hierarchy itself. e.g. the ConfigureForDOS / ConfigureForUnix / ConfigureForX issue.
* When you need to perform very different operations on an object depending upon its type.
Expand All @@ -25,11 +26,13 @@ This pattern can be used:

## Consequences
The good:

* No dependency cycles between class hierarchies.
* No need to recompile all the visitors if a new one is added.
* Does not cause compilation failure in existing visitors if class hierarchy has a new member.

The bad:

* Violates the principle of least surprise or Liskov's Substitution principle by showing that it can accept all visitors but actually only being interested in particular visitors.
* Parallel hierarchy of visitors has to be created for all members in visitable class hierarchy.

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