From my perspective, BEGIN blocks are a form of code smell. In this case, a variation on 'Inappropriate intimacy'.

Several possibilities for a fix stand out:

1. Making that hash a constant.
2. Using inheritance rather than poking stuff into remote namespaces.
3. If the use of the BEGIN block is required to make the code work as need, then a better solution would be to move the require.
4. If the BEGIN block is a precautionary prophylactic, you might as well use cling film, because it is full of holes.

   What if the required module calls the overridden method within its own BEGIN block?

   Once you start the arms race of every programmer putting the bits of their code they think are of paramount importance in BEGIN blocks, soon everybody will be putting everything in BEGIN blocks, and you're back to square one with no solution.

But the most interesting question here I think would be: why are you poking around in there anyway?

That is, what led you in there? What are you trying to do that you're failing to achieve? What error situation are you trying to avoid? What is it that you're really asking for help with?

If this is just an academic exercise of trying to improve your Perl by reading and understanding the internals of some examples, on the basis of what you've posted in isolation, you'd better pick some better examples.

just one more question if I may
where is SOAP::Deserializer::typecast being defined?

I searched on cpan and was not able to find them.

Line -11 to -2 of the code you posted.

...which replaces the definition found in SOAP/Lite.pm

Update: Added second line.

It seems likely (functionally) unnecessary in this specific case. But some prefer not to analyze each specific case to try to convince themselves that it is actually foolproofly unnecessary and so just include BEGIN for such initializations as a "best practice". (The END block is likely just a visual reminder for "this is where you put clean-up code" and "I didn't forget the clean-up code, we just don't need any for this module at this time" -- as such, I might comment it out for the sake of clarity.)

The flow of the above code w/o the BEGIN goes like:

Compile: package iControlTypeCast;
Compile: require SOAP::Lite;                # nothing happens
Compile: my $urnMap;                        # declares the variable
Compile: $urnMap = ...;                     # nothing happens
Compile: sub SOAP::Deserializer::typecast   # makes it possible to cal
+l this
Run:     require SOAP::Lite;                # compiles and then runs S
+OAP/Lite.pm
# During the loading of SOAP::Lite, a whole ton
# of stuff can happen and is likely to happen
Run:     my $urnMap = ...;                  # the variable is /finally
+/ initialized
[download]

In this particular case, it seems unlikely that anything that happens during the loading of SOAP::Lite would lead to SOAP::Deserializer::typecast() being called. But I'd actually have to study the SOAP modules quite a bit more before I was fully convinced of that. It would certainly be bad style for that order of execution, IMHO. But I see no reason to just rely on such an order of execution never arising.

So it seems wise to avoid the window of time where SOAP::Deserializer::typecast() can be called while $urnMap is still not initialized. The BEGIN block avoids exactly that. So, I consider it good style/practice.

hey thanks for the explanation. It looks like i have to study soap::lite more(as well as i can understand that is)
All in all, from my understanding reading this module, only purpose of it is that to make sure key(e.g, {urn:iControl}System.ConfigSync.SaveMode) that user is inputting is in the list of urnMap before allowing it to use.. Am I correct on this?