TAO uses a novel techique to handle data encapsulation, a "scope" command that lets one carry data around in bundles and unpack it on demand.
Example:
scope ::myobj add color variable
scope ::myobj add type static myobj
scope ::myobj add anArray hash
proc testSet newcolor {
scope load ::myobj
set color $newcolor
}
proc testStaticSet ignoredVal {
scope load ::myobj
set type $ignoredVal
}proc testStaticGet {} {
scope load ::myobj
set type $type
}
proc testArraySet {var val} {
scope load ::myobj
set anArray($var) $val
}
proc testArrayGet {var} {
scope load ::myobj
return [lindex [array get anArray $var] 1]
}
proc testGet {} {
scope load ::myobj
return $color
}
testSet green
testGet
> green
testSet blue
testGet
> blue
testArraySet height 20
testArrayGet height
> 20
testStaticSet garbage
# note that changes to "static" vars are not retained
# this is actually correct
testStaticGet
> myobj
Implementation
There are a few pseudocode callouts that are required. One is "object_array", which maps an object name to a global variable. The others are 'get' which returns a value if it exists, or {} otherwise, ladd which adds a value to a list only if it is not present, and ldelete which removes an element from a list.
proc scope {cmnd handle {varname {}} {type variable} {value NULL}} {
upvar #0 [object_array $handle] state
switch $cmnd {
load { uplevel 1 [set state(script)] }
add - del {
array set vartypes [get state(info)]
foreach vtype [array names vartypes] {
ldelete vartypes($vtype) $varname
}
if { $cmnd == "add" } {
ladd vartypes($type) $varname
if { $value != "NULL" } {
set state($varname) $value
}
}
set state(info) [array get vartypes]
scope rebuild $handle
}
rebuild {
set statevar [object_array $handle]
upvar #0 $statevar state
array set meta [get state(info)]
set script {}
###
# this is really only for backward compadibility
# with classes generated for itcl
# enlightened clients will just call objdata(varname)
# directly
###
append script \n "\# LOAD ENCAPSULATED DATA"
append script \n [list set statevar $statevar]
set varlist {}
lappend varlist ${statevar} objdata
set usedvarnames {}
set statics [get meta(static)]
foreach {var} [get meta(hash)] {
if { [lsearch $usedvarnames $var] >= 0 } continue
ladd usedvarnames $var
lappend varlist ${statevar}.${var} $var
}
foreach {var} [get meta(variable)] {
if { [lsearch $usedvarnames $var] >= 0 } continue
ladd usedvarnames $var
lappend varlist ${statevar}($var) $var
}
foreach {globvar localvar} $varlist {
if { [lsearch $statics $localvar] < 0 } {
append script \n [list catch [list upvar #0 $globvar $localvar]]
}
}
foreach {var} $statics {
append script \n [list set $var [get ${statevar}($var)]]
}
set state(script) $script
}
}
}