Hi all,

Perl provides two different constructs to allow a developer to set up a symbol for a value that will be used through out a package, but will not change; these two different constructs are constant and Readonly. Once a constant or a Readonly symbol is defined in a Perl package, it can not be changed else where in the package although it can be used as many times as the developer wishes.

Thus, in Perl there are two standard ways I could define a constant of PI (to six decimal places of accuracy) in my Perl program:

use constant PI => 3.141593;

OR

use Readonly PI => 3.141593;

After using either constant or Readonly to define PI in my program, I can use it as a symbol in my program over and over again, although as the terms imply, I can not change its value.

Here is what I want to know:

• What are the differences between constant and Readonly in Perl?
• Why would I want to use one over the other? Or are they pretty much the same and hence there is no reason to choose one over the other?
• In what version of Perl did constant come into being?
• In what version of Perl did Readonly come into being?
• Which of the two do you use if either and why?

Thanks!

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