The enumeration Item::Type has data-type specific constants for literals:

• STRING_ITEM
• INT_ITEM
• REAL_ITEM
• DECIMAL_ITEM
• DATE_ITEM

This is not friendly to upcoming data type plugins, as they'll need to create their own literals.

We'll do the following:

• Remove the data type specific enumeration values from Item::Type
• Add a new value CONST_ITEM
• Fix the calling code to test for CONST_ITEM, and when it is necessary, detect the data type using other means, such as type_handler(), or by adding new virtual methods into Item or its descendants.

Note, under terms of this task, we'll preserve the old behavior. For example, Item_param::type() (when assigned to an integer value), reports itself as INT_ITEM. This makes parameter work as a position rather than an expression when used in ORDER BY:

  if (order_item->type() == Item::INT_ITEM && order_item->basic_const_item() &&

      !from_window_spec)

This behavior was most likely introduced as a side effect. The new implementation will preserve the old behavior, including side effects like this.