As
revdiablo has said
Readonly is not a core module, whereas
constant is a pragma. There are some shortcomings in the use of the
constant pragma and all of those are in fact well pointed out in the documentation for
Readonly. However
Readonly has a performance penalty and there is at least one 'speed up' module (
Readonly::xs ) on CPAN for it and some useful alternatives. One particularly cunning one is
Scalar::Readonly which although it works only on scalars allows you to programatically 'write enable' a variable, update it and then lock it again. Of course the variable can be tested as well.
I will very rarely use constant, I have never used Readonly. We do some tricks using Scalar::Readonly ocasionally.
jdtoronto
