NAME

CXC::Exporter::Util - Tagged Based Exporting

VERSION

version 0.08

SYNOPSIS

In the exporting code:

  package My::Exporter;
  use CXC::Exporter::Util ':all';

  use parent 'Exporter' # or Exporter::Tiny

  # install sets of constants, with automatically generated
  # enumerating functions
  install_CONSTANTS( {
        DETECTORS => {
            ACIS => 'ACIS',
            HRC  => 'HRC',
        },

        AGGREGATES => {
            ALL  => 'all',
            NONE => 'none',
            ANY  => 'any',
        },
    } );

  # install some functions
  install_EXPORTS(
            { fruit => [ 'tomato', 'apple' ],
              nut   => [ 'almond', 'walnut' ],
            } );

In importing code:

  use My::Exporter   # import ...
   ':fruit',         # the 'fruit' functions
   ':detector',      # the 'detector' functions
   'DETECTORS'       # the function enumerating the DETECTORS constants  values
   'DETECTORS_NAMES' # the function enumerating the DETECTORS constants' names
   ;

  # print the DETECTORS constants' values;
  say $_ for DETECTORS;

  # print the DETECTORS constants' names;
  say $_ for DETECTORS_NAMES;

DESCRIPTION

CXC::Exporter::Util provides tag-centric utilities for modules which export symbols. It doesn't provide exporting services; its sole purpose is to manipulate the data structures used by exporting modules which follow the API provided by Perl's core Exporter module (e.g. Exporter::Tiny).

In particular, it treats %EXPORT_TAGS as the definitive source for information about exportable symbols and uses it to generate @EXPORT_OK and @EXPORT. Consolidation of symbol information in one place avoids errors of omission.

Exporting Symbols

At it simplest, the exporting module calls "install_EXPORTS" with a hash specifying tags and their symbols sets, e.g.,

  package My::Exporter;
  use CXC::Exporter::Util;

  use parent 'Exporter'; # or your favorite compatible exporter

  install_EXPORTS(
            { fruit => [ 'tomato', 'apple' ],
              nut   => [ 'almond', 'walnut' ],
            } );

  sub tomato {...}
  sub apple  {...}
  sub almond {...}
  sub walnut {...}

An importing module could use this via

  use My::ExportingModule ':fruit'; # import tomato, apple
  use My::ExportingModule ':nut';   # import almond, walnut
  use My::ExportingModule ':all';   # import tomato, apple,
                                    #        almond, walnut,

For more complicated setups, %EXPORT_TAGS may be specified first:

  package My::ExportingModule;
  use CXC::Exporter::Util;

  use parent 'Exporter';
  our %EXPORT_TAGS = ( tag => [ 'Symbol1', 'Symbol2' ] );
  install_EXPORTS;

install_EXPORTS may be called multiple times

Exporting Constants

CXC::Exporter::Util provides additional support for creating, organizing and installing constants via "install_CONSTANTS". Constants are created via Perl's constant pragma.

"install_CONSTANTS" is passed sets of constants grouped by tags, e.g.:

  install_CONSTANTS( {
        DETECTORS => {
            ACIS => 'ACIS',
            HRC  => 'HRC',
        },

        AGGREGATES => {
            ALL  => 'all',
            NONE => 'none',
            ANY  => 'any',
        },
   });

   # A call to install_EXPORTS (with or without arguments) must follow
   # install_CONSTANTS;
   install_EXPORTS;

This results in the definition of

the constant functions, i.e.,
```
  ACIS HRC ALL NONE ANY
```
returning their specified values,

functions enumerating the constants' values, i.e.

  DETECTORS -> ( 'ACIS', 'HRC' )
  AGGGREGATES -> ( 'all', 'none', 'any' )

functions enumerating the constants' names, i.e.

  DETECTORS_NAMES -> ( 'ACIS', 'HRC' )
  AGGGREGATES_NAMES -> ( 'ALL', 'NONE', 'ANY' )

The enumerating functions are useful for generating enumerated types via e.g. Type::Tiny:

  Enum[ DETECTORS ]

or iterating:

  say $_ for DETECTORS;

install_CONSTANTS may be called multiple times. If the constants are used later in the module for other purposes, constant definition should be done in a BEGIN block:

  BEGIN {
      install_CONSTANTS( {
          CCD => {nCCDColumns  => 1024, minCCDColumn => 0,},
      } );
  }

  install_CONSTANTS( {
      CCD => {
          maxCCDColumn => minCCDColumn + nCCDColumns - 1,
      } }
  );

  install_EXPORTS;

For more complex situations, the lower level "install_constant_tag" and "install_constant_func" routines may be useful.

SUBROUTINES

install_EXPORTS

  install_EXPORTS( [\%export_tags], [$package], [\%options]  );

Populate $package's @EXPORT and @EXPORT_OK arrays based upon %EXPORT_TAGS and %export_tags.

If not specified, $package defaults to the caller's package.

Available Options:

overwrite => [Boolean]

If the overwrite option is true, the contents of %export_tags will overwrite %EXPORT_TAGS in $package, otherwise %export_tags is merged into %EXPORT_TAGS.

Note that overwriting will remove the tags and symbols installed into %EXPORT_TAGS by previous calls to "install_CONSTANTS".

This defaults to false.

package => [Package Name]

This provides another means of indicating which package to install into. Setting this overrides the optional $package argument.

all => [Boolean | 'auto' ]

This determines whether "install_EXPORTS" creates an all tag based on the contents of %EXPORT_TAGS in $package. Some exporters, such as Exporter::Tiny and Sub::Exporter automatically handle the all tag, but Perl's default Exporter does not.

If set to auto (the default), it will install the all tag if $package is not a subclass of Exporter::Tiny.

(At present I don't know how to determine if Sub::Exporter is used).

This routine does the following in $package based upon %EXPORT_TAGS in $package:

Install the symbols specified via the $EXPORT_TAGS{default} tag into @EXPORT.
Install all of the symbols in %EXPORT_TAGS into @EXPORT_OK.

install_CONSTANTS

  install_CONSTANTS( @specs, ?$package  );

Create sets of constants and make them available for export in $package.

If not specified, $package defaults to the caller's package.

The passed @specs arguments are either hashrefs or arrayrefs and contain one or more set specifications. A set specification consists of a unique identifier and a list of name-value pairs, specified either as a hash or an array. For example,

  @spec = ( { $id1 => \%set1, $id2 => \@set2 },
            [ $id3 => \%set3, $id4 => \@set4 ],
          );

The identifier is used to create an export tag for the set, as well as to name enumerating functions returning constant's names and values. The individual $id, $set pairs are passed to "install_constant_tag"; see that function for more information on how the identifiers are used.

A call to "install_EXPORTS" must be made after the last call to install_CONSTANTS or

The constants won't be added to the exports.
The enumerating functions won't be created.

"install_CONSTANTS" may be called more than once to add symbols to a tag, but don't split those calls across a call to "install_EXPORTS".

In other words,

  # DON'T DO THIS, IT'LL THROW
  install_CONSTANTS( { Foo => { bar => 1 } } );
  install_EXPORTS;
  install_CONSTANTS( { Foo => { baz => 1 } } );
  install_EXPORTS;

  # DO THIS
  install_CONSTANTS( { Foo => { bar => 1 } } );
  install_CONSTANTS( { Foo => { baz => 1 } } );
  install_EXPORTS;

Each call to "install_EXPORTS" installs the enumerating functions for sets modified since the last call to it, and each enumerating function can only be added once.

install_constant_tag

Create and install constant functions for a set of constants. Called either as

install_constant_tag( \@names, $constants, [$package] )

where @names contains

  $tag,
  $fn_values, # optional name of function returning constants' values
  $fn_names,  # optional name of function returning constants' names

and, if not specified,

  $fn_values //= uc($tag);
  $fn_names //= $fn_values . '_NAMES';

install_constant_tag( $fn_values, $constants, [$package] )

where

  $tag = lc($fn_values);
  $fn_names = $fn_values . '_NAMES';

where

$tag: is the name of the tag representing the set of constants
$fn_values: is the name of the function which will return a list of the constants' values
$fn_names: is the name of the function which will return a list of the constants' names
$constants: specifies the constants' names and values, as either a hashref or an arrayref containing name - value pairs.
$package: is the name of the package (the eventual exporter) into which the constants will be installed. It defaults to the package of the caller.

"install_constant_tag" will

use Perl's constant pragma to create a function named name returning value for each name-value pair in $constants.

The functions are installed in $package and their names appended to the symbols in %EXPORT_TAGS with export tag $tag. If $constants is an arrayref they are appended in the ordered specified in the array, otherwise they are appended in random order.
Add a hook so that the next time "install_EXPORTS" is called, Perl's constant pragma will be used to create
- an enumerating function named $fn_values which returns a list of the values of the constants associated with $tag, in the order they were added to $EXPORT_TAGS{$tag}.
- an enumerating function named $fn_names which returns a list of the names of the constants associated with $tag, in the order they were added to $EXPORT_TAGS{$tag}.
These enumerating functions are added to the symbols in %EXPORT_TAGS tagged with contant_funcs.

Just as you shouldn't interleave calls to "install_CONSTANTS" for a single tag with calls to "install_EXPORTS", don't interleave calls to "install_constant_tag" with calls to "install_EXPORTS".

For example, after

  $id = 'AGGREGATES';
  $constants = { ALL => 'all', NONE => 'none', ANY => 'any' };
  install_constant_tag( $id, $constants );
  install_EXPORTS:

The constant functions, ALL, NONE, ANY will be created and installed in the calling package.

A new element will be added to %EXPORT_TAGS with an export tag of aggregates.
```
  $EXPORT_TAGS{aggregates} = [ 'ALL', 'NONE', 'ANY ];
```
A function named AGGREGATES will be created and installed in the calling package. AGGREGATES will return the values
```
  'all', 'none', 'any'
```
(in a random order, as $constants is a hashref).

AGGREGATES will be added to the symbols tagged by constant_funcs in %EXPORT_TAGS
A function named AGGREGATES_NAMES will be created and installed in the calling package. AGGREGATES_NAMES will return the values
```
  'ALL', 'NONE', 'ANY'
```
(in a random order, as $constants is a hashref).

AGGREGATES_NAMES will be added to the symbols tagged by constant_name_funcs in %EXPORT_TAGS

After this, a package importing from $package can

import the constant functions ALL, NONE, ANY via the aggregate tag:
```
   use Package ':aggregate';
```
import the enumerating function AGGREGATES directly, via
```
  use Package 'AGGREGATES';
```
import AGGREGATES via the constant_funcs tag:
```
  use Package ':constant_funcs';
```

As mentioned above, if the first argument to "install_constant_tag" is an arrayref, $tag, $fn_values, and $fn_names may be specified directly. For example,

  $id = [ 'Critters', 'Animals', 'Animal_names' ];
  $constants = { HORSE => 'horse', GOAT   => 'goat' };
  install_constant_tag( $id, $constants );

will create the export tag Critters for the GOAT and HORSE constant functions, an enumerating function called Animals returning

  ( 'horse', 'goat' )

and a function called Animal_names returning

  ( 'HORSE', 'GOAT')

install_constant_tag uses "install_constant_func" to create and install the constant functions which return the constant values.

Because of when enumerating functions are created, all enumerating functions associated with a set will return all of the set's values, regardless of when the function was specified. For example,

  install_constant_tag( 'TAG', { HIGH => 'high' }  );
  install_constant_tag( [ 'TAG', 'ATAG' ], { LOW => 'low' } );

will create functions TAG and ATAG which both return high, low.

install_constant_func( $name, \@values, $caller )

This routine does the following in $package, which defaults to the caller's package.

Create a constant subroutine named $name which returns @values;
Adds $name to the constant_funcs tag in %EXPORT_TAGS.

For example, after calling

  install_constant_func( 'AGGREGATES', [ 'all', 'none', 'any' ]  );

The function AGGREGATES will return all, none, any.
A package importing from $package can import the AGGREGATE constant function via the constant_funcs tag:
```
  use Package ':constant_funcs';
```
or directly
```
  use Package 'AGGREGATES';
```

BUGS

No attempt is made to complain if enumerating functions' names clash with constant function names.

EXAMPLES

Alternate constant generation modules.

To use an alternate constant generation function bypass "install_CONSTANTS" and load things manually.

For example, using enum:

  package My::Exporter;

  use CXC::Exporter::Util ':all';

  our @DaysOfWeek;
  BEGIN{ @DaysOfWeek = qw( Sun Mon Tue Wed Thu Fri Sat ) }
  use enum @DaysOfWeek;
  use constant DaysOfWeek => map { &$_ } @DaysOfWeek;
  install_EXPORTS( { days_of_week => \@DaysOfWeek,
                     constant_funcs => [ 'DaysOfWeek' ],
                    });

and then

  use My::Exporter -days_of_week;

  say Sun | Mon;

Using a constant in the exporting module

When a constant is used in an exporting module (to create another constant, for example), it's tempting to do something like this:

  # DON'T DO THIS
  %CCD = ( minCCDColumn => 0, nCCDColumns = 1024 );
  $CCD{maxCCDColumn} = $CCD{minCCDColumn} + $CCD{nCCDColumns} - 1;
  install_CONSTANTS( { CCD => \%CCD } );
  install_EXPORTS;

Not only is this noisy code, if the hash keys are mistyped, there's an error, which is exactly what constants are supposed to avoid.

Instead, create an initial set of constants in a BEGIN block, which will make them available for the rest of the code:

  BEGIN {
      install_CONSTANTS( {
          CCD => {nCCDColumns  => 1024, minCCDColumn => 0,},
      } );
  }

  install_CONSTANTS( {
      CCD => {
          maxCCDColumn => minCCDColumn + nCCDColumns - 1,
      } }
  );

  install_EXPORTS;

A bit more verbose, but it uses the generated constant functions and avoids errors.

SUPPORT

Bugs

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

Source

Source is available at

  https://gitlab.com/djerius/cxc-exporter-util

and may be cloned from

  https://gitlab.com/djerius/cxc-exporter-util.git

AUTHOR

Diab Jerius <djerius@cpan.org>

COPYRIGHT AND LICENSE

This is free software, licensed under:

  The GNU General Public License, Version 3, June 2007

To install CXC::Exporter::Util, copy and paste the appropriate command in to your terminal.

cpanm

cpanm CXC::Exporter::Util

CPAN shell

perl -MCPAN -e shell
install CXC::Exporter::Util

For more information on module installation, please visit the detailed CPAN module installation guide.

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