Function type

cpp/src/arrow/compute/exec.h:343–349

  }

  const DataType* type() const {
    if (this->is_array_span()) {
      return this->array_span()->type;
    } else {
      return this->array_data()->type.get();
    }
  }

  const ArraySpan* array_span() const { return &std::get<ArraySpan>(this->value); }
  ArraySpan* array_span_mutable() { return &std::get<ArraySpan>(this->value); }