NAME
    Data::Sah::DefaultValue - Default-value rules for Data::Sah

VERSION
    This document describes version 0.004 of Data::Sah::DefaultValue (from
    Perl distribution Data-Sah-DefaultValue), released on 2023-12-09.

SYNOPSIS
     use Data::Sah::DefaultValue  qw(gen_default_value_code);

     # a utility routine: gen_default_value_code
     my $dv = gen_default_value_code(
         default_value_rules => ['Perl::this_mod'],
     );

     my $val = $c->(123);          # unchanged, 123
     my $val = $c->(undef);        # becomes "Some::Module"

DESCRIPTION
    This module generates code to set default value using value rules.

    A value rule is put in
    "Data::Sah::Value::$COMPILER::$TOPIC::$DESCRIPTION" module, for example:
    Data::Sah::Value::perl::Perl::this_mod contains the value "this module"
    (see App::ThisDist for more details on the meaning of "this module").

    Basically, a value rule will provide an expression ("expr_value") that
    return some value.

    The module must contain "meta" subroutine which must return a hashref
    that has the following keys ("*" marks that the key is required):

    *   v* => int (default: 1)

        Metadata specification version. From DefHash. Currently at 4.

    *   summary => str

        From DefHash.

    The module must also contain "value" subroutine which must generate the
    code for default value. The subroutine must accept a hash of arguments
    ("*" indicates required arguments):

    The "value" subroutine must return a hashref with the following keys
    ("*" indicates required keys):

    *   expr_value => str

        Expression in the target language that produces the value.

    *   modules => hash

        A list of modules required by the expressions.

VARIABLES
  $Log_Default_Value_Code => bool (default: from ENV or 0)
    If set to true, will log the generated default-value code (currently
    using Log::ger at trace level). To see the log message, e.g. to the
    screen, you can use something like:

     % TRACE=1 perl -MLog::ger::LevelFromEnv -MLog::ger::Output=Screen \
         -MData::Sah::DefaultValue=gen_default_value_code -E'my $c = gen_default_value_code(...)'

FUNCTIONS
  gen_default_value_code
    Usage:

     gen_default_value_code(%args) -> any

    Generate code to set default value.

    This is mostly for testing. Normally the default value rules will be
    used from Data::Sah via the "x.perl.default_value_rules" or
    "x.js.default_value_rules" or "x.default_value_rules" property.

    This function is not exported by default, but exportable.

    Arguments ('*' denotes required arguments):

    *   default_value_rules => *array[str]*

        A specification of default-value rules to use (or avoid).

        This setting is used to specify which default-value rules to use (or
        avoid) in a flexible way. Each element is a string, in the form of
        either "NAME" to mean specifically include a rule, or "!NAME" to
        exclude a rule.

        To use the default-value rules R1 and R2:

         ['R1', 'R2']

    *   source => *bool*

        If set to true, will return coercer source code string instead of
        compiled code.

    Return value: (any)

ENVIRONMENT
  LOG_SAH_DEFAULT_VALUE_CODE => bool
    Set default for $Log_Default_Value_Code.

HOMEPAGE
    Please visit the project's homepage at
    <https://metacpan.org/release/Data-Sah-DefaultValue>.

SOURCE
    Source repository is at
    <https://github.com/perlancar/perl-Data-Sah-DefaultValue>.

SEE ALSO
    Data::Sah::DefaultValueCommon for detailed syntax of default-value rules
    (explicitly including/excluding rules etc).

    Data::Sah

    Data::Sah::DefaultValueJS

    App::SahUtils

HISTORY
    2021-11-28: Created modelled from Data::Sah::Coerce and
    Data::Sah::Filter to be able to express dynamic default value into
    schema.

AUTHOR
    perlancar <perlancar@cpan.org>

CONTRIBUTING
    To contribute, you can send patches by email/via RT, or send pull
    requests on GitHub.

    Most of the time, you don't need to build the distribution yourself. You
    can simply modify the code, then test via:

     % prove -l

    If you want to build the distribution (e.g. to try to install it locally
    on your system), you can install Dist::Zilla,
    Dist::Zilla::PluginBundle::Author::PERLANCAR,
    Pod::Weaver::PluginBundle::Author::PERLANCAR, and sometimes one or two
    other Dist::Zilla- and/or Pod::Weaver plugins. Any additional steps
    required beyond that are considered a bug and can be reported to me.

COPYRIGHT AND LICENSE
    This software is copyright (c) 2023, 2021 by perlancar
    <perlancar@cpan.org>.

    This is free software; you can redistribute it and/or modify it under
    the same terms as the Perl 5 programming language system itself.

BUGS
    Please report any bugs or feature requests on the bugtracker website
    <https://rt.cpan.org/Public/Dist/Display.html?Name=Data-Sah-DefaultValue
    >

    When submitting a bug or request, please include a test-file or a patch
    to an existing test-file that illustrates the bug or desired feature.