NAME

CXC::constant::setonce - Initialize a constant subroutine once.

VERSION

version 0.01

SYNOPSIS

   use CXC::constant::setonce 'MYCONST';

   # this will die, as MYCONST hasn't been set:
   say MYCONST;

   # this sets MYCONST's value;
   MYCONST( $value );

   # this will succeed
   say MYCONST;

   # and this will die, as MYCONST has already been set
   MYCONST( $value );

DESCRIPTION

This module was written for the case where

1. a constant's value cannot be set until run time

2. attempts to use the constant before its value is set should be fatal.

3. attempts to set the constant's value more than once should be fatal

USAGE

1. Use CXC::constant::setonce as a pragma to declare the constants:

     use CXC::constant::setonce qw( CONST1 CONST 2);

2. Call a constant as a subroutine with an argument to set it:

     CONST1( $value );
     CONST2( $value );

3. Use the constant as you would any other constant:

     if ( CONST1 == 33 ) { ... }

CAVEATS

• If the constant is used prior to being set, any later attempt to set the constant will result in an exception, e.g.

    use CXC::constant::setonce 'CONST';
    eval { CONST }; # will die, eval prevents that from propagating
    CONST($value)   # will die

• There's no way to check if the constant has been set before using it.

SUPPORT

Bugs

Please report any bugs or feature requests to bug-cxc-constant-setonce@rt.cpan.org or through the web interface at: https://rt.cpan.org/Public/Dist/Display.html?Name=CXC-constant-setonce

Source

Source is available at

  https://gitlab.com/djerius/cxc-constant-setonce

and may be cloned from

  https://gitlab.com/djerius/cxc-constant-setonce.git

SEE ALSO

Please see those modules/websites for more information related to this module.

• constant

• constant::defer

AUTHOR

Diab Jerius <djerius@cpan.org>

COPYRIGHT AND LICENSE

This software is Copyright (c) 2023 by Smithsonian Astrophysical Observatory.

This is free software, licensed under:

  The GNU General Public License, Version 3, June 2007