> -----Original Message----- > From: Rob Dixon [mailto:[EMAIL PROTECTED] > Sent: 31 October 2008 11:51 > To: Perl Beginners > Cc: Stewart Anderson > Subject: Re: How to put a global variable in a package, accessible to > users of that package? > > Stewart Anderson wrote: > >> From: mrstevegross [mailto:[EMAIL PROTECTED] > >> > >> I have a package named "Foo" in which I want to define some package- > >> level constants (such as $VAR="soemval"). I want those constants > >> available to users of package Foo, so the following code would work: > >> > >> === foo.pl === > >> package foo; > >> use constant VAR => "someval"; > >> > >> === bar.pl === > >> use foo; > >> print $foo::VAR; > >> > >> It doesn't appear to be working; it compiles ok, but it prints > >> nothing. I thought it would print "someval". > >> > > That looks interesting. How do people use that kind of constant > > assignment. I can see uses for it, but would be interested to hear what > > others use this technique for. > > Take a look at > > perldoc constant > > What the pragma creates is a prototyped subroutine with exactly zero > parameters, > so writing > > use constant PI => 3.14159265359; > > is equivalent to a subroutine > > sub PI() { > 3.14159265359; > } > > However it has a few of advantages over just writing this directly: > > - It is self-documenting, i.e. it is clear that a named constant is being > defined. > > - The Perl compiler has a chance to optimise out the subroutine definition > and > call > > - The implementation could change to something more optimal in the future > without needing to alter any code that uses the pragma > > I hope this helps, > > Rob Thanks :)
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