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=head1 TITLE
Make constants look like variables
=head1 VERSION
Maintainer: Jeremy Howard <[EMAIL PROTECTED]>
Date: 10 August 2000
Version: 1
Mailing List: [EMAIL PROTECTED]
Number: 83
=head1 ABSTRACT
This RFC proposes that the current constant.pm module removed, and
replaced with a syntax allowing any variable to be marked as constant.
=head1 DESCRIPTION
Currently, constants are created in Perl using the constant.pm module:
use constant PI => 3.1415926;
which creates an inlined subroutine:
sub PI () {3.1415926;}
This method of creating constants has three serious drawbacks:
=over 8
=item Can not be interpolated in strings
Whereas variables can be interpolated into strings (e.g. "PI is $Pi"),
subroutines can not be. This makes using constants inconvenient, since
string concatenation must be used.
=item Inconsistant syntax
The sudden appearance of barewords can be quite unsettling to new users.
After becoming told that 'arrays are @name, scalars are $name, ...', the
rule suddenly stops working just because the programmer wants the value to
stay constant.
=item Redundant warnings
In persistant Perl environments such as mod_perl, inlined subroutines
often created the redundant warning 'Constant subroutine PI redefined'.
This has been a frequent source of confusion amongst new mod_perl users.
=back
It is proposed that a new syntax for declaring constants be introduced:
my constant $PI = 3.1415926;
my constant @FIB = (1,1,2,3,5,8,13,21);
my constant %ENG_ERRORS = (E_UNDEF=>'undefined', E_FAILED=>'failed');
Constants can be lexically or globally scoped (or any other new scoping
level yet to be defined).
=head1 IMPLEMENTATION
Constants should have the same behaviour as the do now. They should be
inlined, and constant expressions should be calculated at compile time.
=head1 REFERENCES
perldoc constant; perldoc perlsub (for constant subroutines)
