Wes McKinney created ARROW-621:
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Summary: [C++] Implement an "inline visitor" template that enables
visitor-pattern-like code without virtual function dispatch
Key: ARROW-621
URL: https://issues.apache.org/jira/browse/ARROW-621
Project: Apache Arrow
Issue Type: New Feature
Components: C++
Reporter: Wes McKinney
For performance-sensitive dynamic dispatch, the current visitor pattern may be
suboptimal due to having two virtual function dispatches per invocation. For
example, we might have:
{code}
ArrayVisitor* visitor = ...;
RETURN_NOT_OK(array->Accept(visitor));
{code}
For certain types of visitors, it may be possible to create a reusable pattern
like:
{code:language=c++}
template <typename VISITOR>
Status VisitArrayInline(const Array& array, VISITOR* visitor) {
switch(array->type_id()) {
case UINT8:
return visitor->Visit(static_cast<const UInt8Array&>(array));
...
default:
break;
}
return Status::NotImplemented("Array type not implemented");
}
{code}
It would be useful to have an understanding of how this design pattern
realistically impacts performance in canonical Arrow use cases (e.g. IPC record
batch loading / unloading).
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