Allows to specify concrete type of column in subclasses,
columnByName members return concrete types.
Type of the data described by this struct
For quickly finding a column definition by index.
For quickly finding a column definition by name.
Names of the columns, in the same order as column definitions.
References to the columns
Types of the columns, in the same order as column names and column definitions.
Returns the columns that are not present in the structure.