wjones127 commented on a change in pull request #166:
URL: https://github.com/apache/arrow-cookbook/pull/166#discussion_r830384427
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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:
I've created two new examples. One is a class that generates a random
record batch given a schema and row count, which showcases an approach to
handling nested types.
The other is a class that can sum across columns of varied number types,
which showcases how to use the type traits to avoid repetitive implementations
for similar types.
I think these are better use cases that my original. The first is something
I've seen in the wild (and is also inspired by our internal test functions).
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