class ActiveRecord::ConnectionAdapters::PostgreSQLAdapter::OID::Vector

def initialize(delim, subtype)

pg_types table.
table. +subtype+ is derived from the `typelem` column in the
+delim+ corresponds to the `typdelim` column in the pg_types 
def initialize(delim, subtype)
  @delim   = delim
  @subtype = subtype
end

def type_cast(value)

is to just return the string.
to cast the values. Unfortunately, the current Rails behavior
FIXME: this should probably split on +delim+ and use +subtype+ 
def type_cast(value)
  value
end