TclOO : What is the difference between my and self? - tcl

Question

The documentation probably explains it very well but I do not see the difference between this 2 commands in my case :
method dir {} {
puts "method dir..."
}
method pseudomethod {} {
set vardir [my dir]
set vardir [[self] dir]
}
The only difference I can see is that with [self] I can pass it as an argument in a procedure and not with my.
What is the best solution in my case ?
Both solutions have equal performance ?

Answer 1

The self command (with no extra arguments) is equivalent to self object which returns the current public name of the object that is executing the method (you can rename the object). The self command overall provides access to bits of “runtime” state.
The my command is actually the object's internal name; it's created in each object's instance namespace. You can invoke all exported and non-exported methods via my, unlike with the public name. This makes it useful for both calling your internal methods directly, and also for setting up things like callbacks to internal methods (you'll need something like namespace which or namespace code when setting up the callback).
Unlike with the public name, you can delete the internal name command without automatically destroying the object. It'll likely break code (your methods most probably) if you do that, but the base system allows you to do it.
Aside: Tcl 8.7 includes this helper procedure (which also works in 8.6) for creating callback scripts within methods (the funny name means it gets mapped into your methods automatically as callback):
proc ::oo::Helpers::callback {method args} {
list [uplevel 1 {::namespace which my}] $method {*}$args
}
In this case, if the callback was exported, you'd be able to do this instead:
proc ::oo::Helpers::callback {method args} {
list [uplevel 1 self] $method {*}$args
}
but that would be more vulnerable to rename problems. (In all cases, the uplevel 1 is because we want to run a little bit of name-resolving code in the calling context, not inside the scope of the procedure itself.)

Answer 2

I'm not sure how they are implemented, but one reason you'd want to use my is to access non-exported (private) methods. A demo:
oo::class create Foo {
method PrivateMethod {} {puts "this is PrivateMethod"}
method publicMethod {} {puts "this is publicMethod"}
method test {} {
my publicMethod
my PrivateMethod
[self] publicMethod
[self] PrivateMethod
}
}
then:
% Foo create foo
::foo
% foo test
this is publicMethod
this is PrivateMethod
this is publicMethod
unknown method "PrivateMethod": must be destroy, publicMethod or test
my is the mechanism for an object to invoke its methods.
self is the mechanism for introspection on how the current method was called.
Spend some time with the my and self man pages.