[Xotcl] Deleting objects

From: <MichaelL_at_frogware.com>
Date: Mon, 12 May 2003 10:42:10 -0400

Look at the following code, which is meant to be a stripped-down and
simplified version of my real code:

Class DatabaseMgr

DatabaseMgr instproc openDatabase {} {
    Database [self]::db
}

Class Database

Database instproc init {} {
    puts "init [self]"
}

Database instproc destroy {} {
    puts "destroy [self]"
}

DatabaseMgr dbmgr

dbmgr openDatabase

dbmgr::db info class
dbmgr::db destroy
dbmgr::db info class

The second call to "info class" should fail but doesn't. That's because
the object isn't actually destroyed. (In my real code the objects have
dynamically generated names; I used the static names to simplify the
example.)

The above style is similar to the style of code used in xoRBAC (eg,
factories & self-destruction) so I'd be surprised if it too wasn't leaking
objects.

After the above code run this code:

dbmgr info class
dbmgr destroy
dbmgr info class

Now both dbmgr and dbmgr::db are destroyed--but note that the "destructor"
gets called twice at this point!

By contrast, the following example (which also uses nested/aggregated
objects) succeeds (which is to say that the second call to "info class"
fails):

Object instproc doSomethingAndDie {} {[self] destroy}
set xxx [Object new]
set yyy [Object new -childof $xxx]
set zzz [Object new -childof $yyy]
puts "[$yyy info class]"
$yyy doSomethingAndDie
puts "[$yyy info class]"