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The problem with your original version is that the use constant executes at compile time, but the regular expression executes at run time - i.e. after everything has been compiled - so it's setting the $CONF_PATH variable too late. To see the difference between compile time and run time, run this:

print "World\n"; BEGIN { print "Hello " };

And the use keyword (plus its friend no) runs conceptually in a BEGIN block.

A do { ... } block provides a neat solution:

package mylib; use constant { MODULE_PATH => __FILE__, CONF_PATH => do { $_ = __FILE__; s/pm$/conf/i; $_ }, }; print CONF_PATH;

If your perl is fairly recent, you can do away with do and use /r.

package mylib; use constant { MODULE_PATH => __FILE__, CONF_PATH => (__FILE__ =~ s/pm$/conf/ir), }; print CONF_PATH;
perl -E'sub Monkey::do{say$_,for@_,do{($monkey=[caller(0)]->[3])=~s{::}{ }and$monkey}}"Monkey say"->Monkey::do'

In reply to Re: BEGIN block and failure to initialize constants by tobyink
in thread BEGIN block and failure to initialize constants by temporal

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