drin commented on code in PR #227: URL: https://github.com/apache/arrow-cookbook/pull/227#discussion_r932537934
########## cpp/source/compute.rst: ########## @@ -0,0 +1,151 @@ +.. Licensed to the Apache Software Foundation (ASF) under one +.. or more contributor license agreements. See the NOTICE file +.. distributed with this work for additional information +.. regarding copyright ownership. The ASF licenses this file +.. to you under the Apache License, Version 2.0 (the +.. "License"); you may not use this file except in compliance +.. with the License. You may obtain a copy of the License at + +.. http://www.apache.org/licenses/LICENSE-2.0 + +.. Unless required by applicable law or agreed to in writing, +.. software distributed under the License is distributed on an +.. "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY +.. KIND, either express or implied. See the License for the +.. specific language governing permissions and limitations +.. under the License. + +==================================== +Defining and Using Compute Functions +==================================== + +This section contains (or will contain) a number of recipes illustrating how to +define new "compute functions" or how to use existing ones. Arrow contains a "Compute +API," which primarily consists of a "registry" of functions that can be invoked. +Currently, Arrow populates a default registry with a variety of useful functions. The +recipes provided in this section show some approaches to define a compute function as well +as how to invoke a compute function by name, given a registry. + + +.. contents:: + +Invoke a Compute Function +========================= + +When invoking a compute function, the function must exist in a function registry. In this +recipe, we use `CallFunction()` to invoke the function with name "named_scalar_fn". + +.. recipe:: ../code/compute_fn.cc InvokeByCallFunction + :caption: Use CallFunction() to invoke a compute function by name + :dedent: 2 + +.. note:: + This method allows us to specify arguments as a vector and a custom ExecContext. + +If an `ExecContext` is not passed to `CallFunction` (it is null), then the default +FunctionRegistry will be used to call the function from. + +If we have defined a convenience function that wraps `CallFunction()`, then we can call +that function instead. Various compute functions provided by Arrow have these convenience +functions defined, such as `Add` or `Subtract`. + +.. recipe:: ../code/compute_fn.cc InvokeByConvenienceFunction + :caption: Use a convenience invocation function to call a compute function + :dedent: 2 + + +Adding a Custom Compute Function +================================ + +To make a custom compute function available, there are 3 primary steps: + +1. Define kernels for the function (these implement the actual logic) + +2. Associate the kernels with a function object + +3. Add the function object to a function registry + + +Define Function Kernels +----------------------- + +A kernel is a particular function that implements desired logic for a compute function. Review Comment: mmmm.. I wrote the paragraph to help contextualize what the recipe covers and what it doesn't. Also to implicitly hint at why the kernel function is named `Exec` and clarify that both an execution kernel and intialization kernel are basically just functions associated with "the compute function". Also that they are associated as a pair, so initialization and execution kernels are not dispatched individually. I definitely see your point, so I don't know if I should just move this to some other documentation which may not yet exist or if I should leave it here to be moved later. -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected]
