Dear monks,

Just a short meditation to alert you to the evils that lurk in POSIX constants. For example 

% perl -MPOSIX=CHAR_MAX -wle 'print( CHAR_MAX )'
127
% perl -MPOSIX=CHAR_MAX -wle 'print( CHAR_MAX + 1 )'
127

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No difference between printing CHAR_MAX and CHAR_MAX + 1! A quick consultation with MO=Deparse provides the necessary insight: 
% perl -MPOSIX=CHAR_MAX -MO=Deparse,-p -e 'print( CHAR_MAX + 1 )'
print(CHAR_MAX(1));
-e syntax OK

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But check this out: 
% perl -Mconstant=CHAR_MAX,127 -wle 'print( CHAR_MAX + 1 )'
128
% perl -Mconstant=CHAR_MAX,127 -wle 'print( CHAR_MAX( 1 ) )'
Too many arguments for main::CHAR_MAX at -e line 1, at end of line
Execution of -e aborted due to compilation errors.

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It appears that rolling one's own CHAR_MAX with constant produces a more civilized item than POSIX::CHAR_MAX.

I haven't delved into the POSIX module to get to the bottom of this but we can conclude that, although POSIX constants are subs, they don't behave as nicely as those produced with the constant pragma. They can bite, so watch out.

Thanks to tye for the words o' wisdom.

the lowliest monk

In reply to Beware of POSIX constants by tlm

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