Tcl: Setting a private variable of an owned instance within a class - tcl

Question

Suppose the following code declarations:
itcl::class ObjectA {
private variable m_ownedObject
private variable m_someVariable
constructor {} \
{
set m_ownedObject [ObjectA #auto]
}
protected method SetSomeVariable {newVal} {
set m_someVariable $newVal
}
public method SomeMethod{} {
$m_ownedObject SetSomeVariable 5
}
}
This is the only way I know how to modify m_someVariable from within SomeMethod on m_ownedObject. In other languages (say C/C++/C#/Java to name a few), I'm pretty sure I could just say something like:
m_ownedObject.m_someVariable = 5
Is there a way to do something like this in tcl, or do I always need to create protected getters and setters? Hopefully this is reasonably clear.

Answer 1

You cannot directly do what you're asking for in itcl. However, this being Tcl, you can work around that, and directly set the member variable from anywhere. I use a helper routine called memv which you pass an instance and a variable name, and it returns a "reference" to that variable.
This obviously bypasses the private/protected mechanisms that Itcl set up, so you're violating abstractions using them. It's your call whether you want to use it. I find it invaluable for debugging, but don't it in production code.
The example usage is:
set [memv m_ownedObject m_someVariable] 5
The code for memv is:
proc memv {obj varname} {
# have to look up the variable, which might be in a base class
# so do 'info variable' to get that, and the full name is the 3rd element
# next two lines handle pulling apart an array
set aindex ""
regexp -- {^(.+)\((.+)\)$} $varname ignore varname aindex
set var [lindex [$obj info variable $varname] 2]
if {$aindex == ""} {
return [list #itcl $obj $var]
} else {
return [list #itcl $obj $var\($aindex\)]
}
}
Similarly, I have a helper routine named memv which allows you to call any method (including private and protected methods). It's usage is similar
[memf m_ownedObject SetSomeVariable] 5
And it's code is:
proc memf {obj fcnname} {
set f [$obj info function $fcnname]
if {[llength $f] != 5} {
error "expected '$obj info function $fcnname' to return something like 'private proc ::namespace::name args {...}' but got: $f"
}
set fullname [lindex [$obj info function $fcnname] 2]
set namespace [namespace qualifiers $fullname]
set function [namespace tail $fullname]
return [itcl::code -namespace $namespace $obj $function]
}

Answer 2

$m_ownedObject configure -m_someVariable 5

Answer 3

If you're declaring a variable as private, means that can be only accessed from within the class. And that's also valid for C/C++/Java ... so I'm not sure what are you expecting.
Anyway Tcl is a dynamic language, so you can do something like that.
itcl::class tclass {
foreach v {time distance} {
method get$v {} [subst -nocommands { return [subst $$v] }]
method set$v nuval [subst -nocommands { set $v \$nuval } ]
protected variable $v "Var $v"
}
}
And it will create all the getters and setters that you need ;)
You can find more info here: http://wiki.tcl.tk/17667