In the oop lab, it mentions:
How to extend a class:
0. add coextend parent to the new class script
1. call parent create with: create_parent_ f.
2. do your create stuff AFTER you create your parent
3. do your destroy stuff BEFORE you destroy your parent
4. call parent destroy with: destroy_parent_ f.
5. call parent methods with: method_parent_ f.
This is an elegent method, but has a minor restriction.
When a script is locked, "method_parent_ f." is "method_parent_" itself
because it is not possible to examine the content of method_parent_
once the script is locked.
I found a workaround to this problem using redefining.
NB. original script using f.
coclass 'pbcx'
coextend 'pbc'
create=: verb define
create_pbc_ y. NB. our parent's create
NB. do our create stuff here
0
)
destroy=: verb define
NB. destroy our stuff here
destroy_pbc_ f. y. NB. our parent's destroy
)
getfirst=: verb def 'get {. keys'
NB. modified script using redefining
coclass 'pbcx'
coextend 'pbc'
pbc_create_pbc_=: create_pbc_ NB. redefining hidden name
pbc_destroy_pbc_=: destroy_pbc_ NB. redefining hidden name
create=: verb define
pbc_create y. NB. our parent's create
NB. do our create stuff here
0
)
destroy=: verb define
NB. destroy our stuff here
pbc_destroy y. NB. our parent's destroy
)
getfirst=: verb def 'get {. keys'
NB. looking at names accessible from bcx
create__bcx1 ''
copathnlx__bcx1 ''
+-----------+--+----+---+
|COCREATOR |16| | |
+-----------+--+----+---+
|data |16| |pbc|
+-----------+--+----+---+
|keys |16| |pbc|
+-----------+--+----+---+
|sn |16| |pbc|
+-----------+--+----+---+
|COCLASSPATH| |pbcx|pbc|
+-----------+--+----+---+
|create | |pbcx|pbc|
+-----------+--+----+---+
|destroy | |pbcx|pbc|
+-----------+--+----+---+
|getfirst | |pbcx| |
+-----------+--+----+---+
|get | | |pbc|
+-----------+--+----+---+
|pbc_create | | |pbc|
+-----------+--+----+---+
|pbc_destroy| | |pbc|
+-----------+--+----+---+
|put | | |pbc|
+-----------+--+----+---+
It can be seen that pbc's "create" and "destroy" are hidden by pbcx,
but "pbc_create" and "pbc_destroy" are accessible by pbcx. Moreover
no suffix "_pbc_" is needed so that it will not switch locale.
Note.
1)
Depending on whether you intended to lock the script, you may use either method
to coextend a class.
2)
You need either "method_parent_ f." or "parent_method" or other workarounds iff
the class has its own "method" and also needs to access parent's "method"
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