Facility for creating read-only scalars, arrays, hashes
Description
Readonly provides a facility for creating non-modifiable scalars,
arrays, and hashes. Any attempt to modify a Readonly variable throws
an exception.
Readonly:
* Creates scalars, arrays (not lists), and hashes
* Creates variables that look and work like native perl variables
* Creates global or lexical variables
* Works at run-time or compile-time
* Works with deep or shallow data structures
* Prevents reassignment of Readonly variables
