[jira] [Created] (ARROW-13167) [C++] Type determination kernels ("type", "type_id")

["Ian Cook (Jira)" <ji...@apache.org>]

Ian Cook created ARROW-13167:
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             Summary: [C++] Type determination kernels ("type", "type_id")
                 Key: ARROW-13167
                 URL: https://issues.apache.org/jira/browse/ARROW-13167
             Project: Apache Arrow
          Issue Type: Improvement
          Components: C++
            Reporter: Ian Cook


The Arrow C++ library exposes an API for determining the data type of an expression, but it is exposed as a method of the expression class and it requires that the user pass a schema as an argument to the method. This is inconvenient; for example, we have had to write some inconsistent code in the R bindings to make expression objects carry schemas along with them and then pass the schemas to derivative expressions, unifying schemas as needed for derivative expressions that take 2+ expressions as arguments.

This would be much cleaner if we could use the kernel function calling interface to call a unary {{type_id}} function that would simply determine the type of its input datum and return a scalar integer value from the data type enum indicating the its data type. It would be convenient to also have a version of this that returned the string description of the data type; I think this could be named {{type}}.



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