obj'c`categories vs ada`child pkg's

2.14: adda/cstr/obj'c`categories vs ada`child pkg's:
. obj'c`categories like ada`child pkg's ?
categories are more modifiable:
you can override old def's
even without a recompile of old clients,
because classes are linked at run time, not compile time .
. pkg's are hardwired
but the compiler keeps a record of how
compilation units are org'd,
and this record can be modified,
so a parent pkg body
stays uncompiled and un-overridden
while a parent pkg head
can have child pkg's appended to it .