Hi, By looking into the code of arrow compute, I found there it uses `TypeHolder` [1], and expression might call `GetTypes` to get the input or output types. The document for `TypeHolder` says that it's a container for dynamically created `shared_ptr<DataType>`. However, my view is:
1. It's widely used, and might store non-owned types(e.g [2]) 2. There are some type factory for lots of data type, like [3], so non-nested types tent to be used with singleton I wonder that when would `TypeHolder` has owned types, when would them have non-owned types, and would some primitive types like int8, int16 or types like string shares the same underlying pointer? Thanks, Xuwei Fu [1] https://github.com/apache/arrow/blob/main/cpp/src/arrow/type.h#L215 [2] https://github.com/apache/arrow/blob/main/cpp/src/arrow/compute/expression_internal.h#L47 [3] https://github.com/apache/arrow/blob/main/cpp/src/arrow/type.cc#L2510
