[GitHub] [arrow-cookbook] nirandaperera commented on a change in pull request #166: [C++] Add TypeVisitor example

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nirandaperera commented on a change in pull request #166:
URL: https://github.com/apache/arrow-cookbook/pull/166#discussion_r829544343



##########
File path: cpp/source/basic.rst
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@@ -48,3 +48,29 @@ boilerplate for you.  It will run the contained expression and check the resulti
 .. recipe:: ../code/basic_arrow.cc ReturnNotOk
   :caption: Using ARROW_RETURN_NOT_OK to check the status
   :dedent: 2
+
+
+Using the Visitor Pattern
+=========================
+
+Arrow classes like DataType, Scalar, and Array have specialized subclasses for
+each Arrow type. In order to work with them, use the visitor pattern. These 
+types provide an Accept method and have associated Visitor classes.
+
+As an example, below we implement a :cpp:class:`arrow::TypeVisitor` that counts
+the number of  primitive and nested types.
+
+To implement a TypeVisitor we have to implement a Visit method for every possible
+DataType we wish to handle. Fortunately, we can often use templates and type
+traits to make this less verbose.
+
+.. literalinclude:: ../code/basic_arrow.cc
+   :language: cpp
+   :linenos:
+   :start-at: class TypeCountVisitor
+   :end-at: };  // TypeCountVisitor
+   :caption: TypeVisitor that counts nested and non-nested types

Review comment:
       IMO https://github.com/apache/arrow/pull/11886 was a really good example of a `TypeVisitor` :-) 




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