Re^9: The Null Mull (or, when OO needs more O)

I understand that overloading them is asking for trouble. I want to know how to ask for trouble, if doing that is what I want to do. Of course, one shouldn't do this in production. However, it may be appropriate to do it in some really weird circumstance. Knowing how to do it is only half the battle - knowing when not to do it is the other half.

So, how do you do it? :-)

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Comment on Re^9: The Null Mull (or, when OO needs more O)

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Re^10: The Null Mull (or, when OO needs more O) by diotalevi (Canon) on Dec 01, 2004 at 02:50 UTC
You use the `&Internals::SvREADONLY( \ undef, 0 )` trick to allow you to overwrite it. I'm not actually sure how you'd get another undef to reset the global undef value back to undef. Also, there are a lot of places where assumptions are made that the canonical undefined value is always undefined and has some expected characteristics at a C level. You'll run into various built in functions that test for truth and definedness in ways that will break after altering undef. I'm pretty sure of that anyway. So if you change PL_sv_undef then you probably also need to read all of the source for the build-in functions you're using and be sure that you control all the user-side perl that will have your change in scope. This whole thing sounds so violently wrong that even setting $[ is trivial by comparison. I can't imagine any circumstance where you'd want to invoke so much concentrated chaos. This isn't like using a source filter or some behaviour that is expected to be naughty. So between just us bears, this is probably leads to justifiable homicide. I really don't think there is any sane way to use this. It probably doesn't belong in your bag of tricks.	[reply] [d/l]

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Re^10: The Null Mull (or, when OO needs more O)
by diotalevi (Canon) on Dec 01, 2004 at 02:50 UTC

You use the &Internals::SvREADONLY( \ undef, 0 ) trick to allow you to overwrite it. I'm not actually sure how you'd get another undef to reset the global undef value back to undef. Also, there are a lot of places where assumptions are made that the canonical undefined value is always undefined and has some expected characteristics at a C level. You'll run into various built in functions that test for truth and definedness in ways that will break after altering undef. I'm pretty sure of that anyway. So if you change PL_sv_undef then you probably also need to read all of the source for the build-in functions you're using *and* be sure that you control all the user-side perl that will have your change in scope.

This whole thing sounds so violently wrong that even setting $[ is trivial by comparison. I can't imagine any circumstance where you'd want to invoke so much concentrated chaos. This isn't like using a source filter or some behaviour that is expected to be naughty. So between just us bears, this is probably leads to justifiable homicide. I really don't think there is any sane way to use this. It probably doesn't belong in your bag of tricks.

[reply]
[d/l]