Add libcudf public/detail API pattern to developer guide

cpp/doxygen/developer_guide/DEVELOPER_GUIDE.md

@@ -1,4 +1,4 @@
-# libcudf C++ Developer Guide
+# libcudf C++ Developer Guide {#DEVELOPER_GUIDE}
 
 This document serves as a guide for contributors to libcudf C++ code. Developers should also refer
 to these additional files for further documentation of libcudf best practices.
@@ -469,7 +469,7 @@ libcudf throws under different circumstances, see the [section on error handling
 
 # libcudf API and Implementation
 
-## Streams
+## Streams {#streams}
 
 libcudf is in the process of adding support for asynchronous execution using
 CUDA streams. In order to facilitate the usage of streams, all new libcudf APIs
@@ -486,33 +486,37 @@ use only asynchronous versions of CUDA APIs with the stream parameter.
 
 In order to make the `detail` API callable from other libcudf functions, it should be exposed in a
 header placed in the `cudf/cpp/include/detail/` directory.
+The declaration is not necessary if no other libcudf functions call the `detail` function.
 
 For example:
 
 ```c++
 // cpp/include/cudf/header.hpp
-void external_function(...);
+void external_function(...,
+  rmm::cuda_stream_view stream      = cudf::get_default_stream(),
+  rmm::device_async_resource_ref mr = rmm::mr::get_current_device_resource());
 
 // cpp/include/cudf/detail/header.hpp
 namespace detail{
-void external_function(..., rmm::cuda_stream_view stream)
+void external_function(..., rmm::cuda_stream_view stream, rmm::device_async_resource_ref mr)
 } // namespace detail
 
 // cudf/src/implementation.cpp
 namespace detail{
-    // Use the stream parameter in the detail implementation.
-    void external_function(..., rmm::cuda_stream_view stream){
-        // Implementation uses the stream with async APIs.
-        rmm::device_buffer buff(...,stream);
-        CUDF_CUDA_TRY(cudaMemcpyAsync(...,stream.value()));
-        kernel<<<..., stream>>>(...);
-        thrust::algorithm(rmm::exec_policy(stream), ...);
-    }
+// Use the stream parameter in the detail implementation.
+void external_function(..., rmm::cuda_stream_view stream, rmm::device_async_resource_ref mr){
+  // Implementation uses the stream with async APIs.
+  rmm::device_buffer buff(..., stream, mr);
+  CUDF_CUDA_TRY(cudaMemcpyAsync(...,stream.value()));
+  kernel<<<..., stream>>>(...);
+  thrust::algorithm(rmm::exec_policy(stream), ...);
+}
 } // namespace detail
 
-void external_function(...){
-    CUDF_FUNC_RANGE(); // Generates an NVTX range for the lifetime of this function.
-    detail::external_function(..., cudf::get_default_stream());
+void external_function(..., rmm::cuda_stream_view stream, rmm::device_async_resource_ref mr)
+{
+  CUDF_FUNC_RANGE(); // Generates an NVTX range for the lifetime of this function.
+  detail::external_function(..., stream, mr);
 }
 ```
 
@@ -703,28 +707,28 @@ The preferred style for how inputs are passed in and outputs are returned is the
     - `column_view const&`
   - Tables:
     - `table_view const&`
-    - Scalar:
-        - `scalar const&`
-    - Everything else:
-       - Trivial or inexpensively copied types
-          - Pass by value
-       - Non-trivial or expensive to copy types
-          - Pass by `const&`
+  - Scalar:
+    - `scalar const&`
+  - Everything else:
+    - Trivial or inexpensively copied types
+      - Pass by value
+    - Non-trivial or expensive to copy types
+      - Pass by `const&`
 - In/Outs
   - Columns:
     - `mutable_column_view&`
   - Tables:
     - `mutable_table_view&`
-    - Everything else:
-        - Pass by via raw pointer
+  - Everything else:
+    - Pass by via raw pointer
 - Outputs
   - Outputs should be *returned*, i.e., no output parameters
   - Columns:
     - `std::unique_ptr<column>`
   - Tables:
     - `std::unique_ptr<table>`
-    - Scalars:
-        - `std::unique_ptr<scalar>`
+  - Scalars:
+    - `std::unique_ptr<scalar>`
 
 
 ### Multiple Return Values
@@ -908,6 +912,10 @@ functions that are specific to columns of Strings. These functions reside in the
 namespace. Similarly, functionality used exclusively for unit testing is in the `cudf::test::`
 namespace.
 
+The public function is expected to contain a call to `CUDF_FUNC_RANGE()` followed by a call to
+a `detail` function with same name and parameters as the public function.
+See the [Streams](#streams) section for an example of this pattern.
+
 ### Internal
 
 Many functions are not meant for public use, so place them in either the `detail` or an *anonymous*