lidavidm commented on a change in pull request #12717:
URL: https://github.com/apache/arrow/pull/12717#discussion_r836664537
##########
File path: docs/source/cpp/api/utilities.rst
##########
@@ -56,3 +56,132 @@ Compression
.. doxygenclass:: arrow::util::Decompressor
:members:
+
+Visitors
+========
+
+.. doxygenfunction:: arrow::VisitTypeInline
+ :project: arrow_cpp
+
+.. doxygenfunction:: arrow::VisitTypeIdInline
+ :project: arrow_cpp
+
+.. doxygenfunction:: arrow::VisitScalarInline
+ :project: arrow_cpp
+
+.. doxygenfunction:: arrow::VisitArrayInline
+ :project: arrow_cpp
+
+
+.. _type-traits:
+
+Type Traits
+===========
+
+These types provide relationships between Arrow types at compile time.
:cpp:type:`TypeTraits`
+maps Arrow DataTypes to other types, and :cpp:type:`CTypeTraits ` maps C types
to
+Arrow types.
+
+TypeTraits
+----------
+
+Each specialized type defines the following associated types:
+
+.. cpp:type:: TypeTraits::ArrayType
+
+ Corresponding :doc:`Arrow array type </cpp/api/array.rst>`
+
+.. cpp:type:: TypeTraits::BuilderType
+
+ Corresponding :doc:`array builder type </cpp/api/builders.rst>`
+
+.. cpp:type:: TypeTraits::ScalarType
+
+ Corresponding :doc:`Arrow scalar type </cpp/api/scalar.rst>`
+
+.. cpp:var:: TypeTraits::is_parameter_free
+
+ Whether the type has any type parameters, such as field types in nested types
+ or scale and precision in decimal types.
+
+
+In addition, the following are defined for many but not all of the types:
+
+.. cpp:type:: TypeTraits::CType
+
+ Corresponding C type. For example, ``int64_t`` for ``Int64Array``.
+
+.. cpp:type:: TypeTraits::TensorType
+
+ Corresponding :doc:`Arrow tensor type </cpp/api/tensor.rst>`
+
+.. cpp:function:: static inline constexpr int64_t bytes_required(int64_t
elements)
+
+ Return the number of bytes required for given number of elements. Defined
for
+ types with a fixed size.
+
+.. cpp:function:: static inline std::shared_ptr<DataType>
TypeTraits::type_singleton()
+
+ For types where is_parameter_free is true, returns an instance of the data
type.
+
+
+.. doxygengroup:: type-traits
+ :content-only:
+ :members:
+ :undoc-members:
+
+CTypeTraits
+-----------
+
+Each specialized type defines the following associated types:
+
+.. cpp:type:: CTypeTraits::ArrowType
+
+ Corresponding :doc:`Arrow type </cpp/api/datatype.rst>`
+
+.. doxygengroup:: c-type-traits
+ :content-only:
+ :members:
+ :undoc-members:
+
+
+.. _type-predicates-api:
+
+Type Predicates
+---------------
+
+Type predicates that can be used with templates. Predicates of the form
``is_XXX``
+resolve to constant boolean values, while predicates of the form
``enable_if_XXX``
+resolve to the second type parameter ``R`` if the first parameter ``T`` passes
+the test.
+
+Example usage:
+
+.. code-block:: cpp
+
+ template<typename TypeClass>
+ arrow::enable_if_number<TypeClass, RETURN_TYPE> my_function(const TypeClass&
type) {
Review comment:
nit here and below as well, try to follow the Arrow convention?
##########
File path: docs/source/cpp/datatypes.rst
##########
@@ -66,3 +66,139 @@ To instantiate data types, it is recommended to call the
provided
type = arrow::timestamp(arrow::TimeUnit::MICRO);
// A list type of single-precision floating-point values
type = arrow::list(arrow::float32());
+
+
+
+Type Traits
+-----------
+
+Writing code that can handle concrete :class:`arrow::DataType` subclasses
would
+be verbose, if it weren't for type traits. Similar to the type traits provided
+in `std::type_traits <https://en.cppreference.com/w/cpp/header/type_traits>`_,
+Arrow's type traits map the Arrow data types to the specialized array, scalar,
+builder, and other associated types. For example, the Boolean type has traits:
Review comment:
Just to be precise, they are similar in _concept_ (the C++ utilities
look quite different after all) but for both the main goal is to make
metaprogramming easier.
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