Re^2: The Null Mull (or, when OO needs more O)

Hrmm ... 5.8.4/Solaris doesn't seem to do the right thing.

BEGIN {
    &Internals::SvREADONLY(\undef, 0);
    undef = 42;
    &Internals::SvREADONLY(\undef, 1);
}

my $x = undef;

print( ((undef) ? 'True' : 'False'), $/);
print( ((defined undef) ? 'True' : 'False'), $/);
print( (($x) ? 'True' : 'False'), $/);
print( ((defined $x) ? 'True' : 'False'), $/);

--------------

True
True
False
False
[download]

Maybe the code isn't actually affecting SV_UNDEF as you think ...

Being right, does not endow the right to be rude; politeness costs nothing.
Being unknowing, is not the same as being stupid.
Expressing a contrary opinion, whether to the individual or the group, is more often a sign of deeper thought than of cantankerous belligerence.
Do not mistake your goals as the only goals; your opinion as the only opinion; your confidence as correctness. Saying you know better is not the same as explaining you know better.

Comment on Re^2: The Null Mull (or, when OO needs more O) Download Code

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Re^3: The Null Mull (or, when OO needs more O) by hardburn (Abbot) on Nov 29, 2004 at 19:07 UTC
I just ran your code on 5.8.4 i686-Linux with the same result you did. I'm not sure what is going on here--someone with more understanding of the internals is needed. My guess is that undef isn't staying shared like I expected it would. It does work with taking a reference to undef, but this breaks the transparency I was hoping for: `BEGIN { &Internals::SvREADONLY(\undef, 0); undef = 42; &Internals::SvREADONLY(\undef, 1); } my $x = ${ \undef }; print( ((undef) ? 'True' : 'False'), $/); print( ((defined undef) ? 'True' : 'False'), $/); print( (($x) ? 'True' : 'False'), $/); print( ((defined $x) ? 'True' : 'False'), $/); print $x, $/; __OUTPUT__ True True True True 42` [download] "There is no shame in being self-taught, only in not trying to learn in the first place." -- Atrus, Myst: The Book of D'ni.	[reply] [d/l]
Re^4: The Null Mull (or, when OO needs more O) by dragonchild (Archbishop) on Nov 29, 2004 at 19:29 UTC
`BEGIN { &Internals::SvREADONLY(\undef, 0); undef = 42; &Internals::SvREADONLY(\undef, 1); } use constant UNDEF => ${ \undef }; my $x = UNDEF;` [download] Which is probably better because you're commenting that you did something funky with undef. shrugs Being right, does not endow the right to be rude; politeness costs nothing. Being unknowing, is not the same as being stupid. Expressing a contrary opinion, whether to the individual or the group, is more often a sign of deeper thought than of cantankerous belligerence. Do not mistake your goals as the only goals; your opinion as the only opinion; your confidence as correctness. Saying you know better is not the same as explaining you know better.	[reply] [d/l]