# ABSTRACT: Validating function/method parameters using Data::Sah
# PODNAME: Data::Sah::Manual::ParamsValidating



=encoding UTF-8

=head1 NAME

Data::Sah::Manual::ParamsValidating - Validating function/method parameters using Data::Sah

=head1 VERSION

This document describes version 0.910 of Data::Sah::Manual::ParamsValidating (from Perl distribution Data-Sah), released on 2021-08-01.


There are several choices when it comes to validating function/method parameters
using L<Sah> schemas and L<Data::Sah>. The job of Data::Sah is just to generate
Perl code from a L<Sah> schema. The Perl code can be integrated into your code
in several ways. The final result might or might not need Data::Sah itself.

The document is divided into two parts depending on where the Sah schemas are


One recommended way to put the schemas are in the L<Rinci> function metadata.
With Rinci metadata you specify more than just types/constraints for your
function parameters/arguments, including: summary & description, return value,
command-line short options, tab completion, and so on.

Once you have your Rinci metadata, e.g.:

 $SPEC{foo} = {
     v => 1.1,
     summary => 'Does foo',
     args => {
         a1 => {
             summary => 'First argument',
             schema => 'int*',
             req => 1,
         a2 => {
             summary => 'Second argument',
             schema => ['array', of=>'int*', min_len=>1],
             default => [1],
 sub foo {
     my %args = @_;

You can decide whether you want to depend on Data::Sah or not during runtime.

=head2 Dist::Zilla::Plugin::Rinci::Validate

If you do not want to depend on Data::Sah, what you can do is insert the
generated validator code:

     my %args = @_; # VALIDATE_ARGS

This requires that your code be organized as a Perl distribution, and you use
L<Dist::Zilla> to build your distribution, and you use the
L<Dist::Zilla::Plugin::Rinci::Validate> plugin to scan for the C<#
VALIDATE_ARGS> labels and insert the validator code there (all in one long line,
as to not mess with line numbers). Also, the validator code will only be present
in the built version of your code. But this way, you can avoid an extra sub call
to the validator code and the validator code no longer needs need Data::Sah. The
the overhead of compilation from Sah schema to Perl code is moved into
distribution build time.

If you use this method, it is advisable that you also put this attribute in your
Rinci metadata (the dzil plugin will remind you):

 'x.func.validate_args' => 1

This is to express that your function already performs argument validation and
other tools/frameworks (e.g. L<Perinci::CmdLine::Lite> or
L<Perinci::Sub::Wrapper>, see below) can skip doing argument validation again.
Forgetting to add this attribute is not dangerous, it just means you're
validating twice (where once is already enough).

=head2 Perinci::Sub::ValidateArgs

If you find the above method too cumbersome, you can also generate the validator
dynamically using L<Perinci::Sub::ValidateArgs>.

 use Perinci::Sub::ValidateArgs;

 $SPEC{foo} = {
 sub foo {
     state $validator = gen_args_validator();
     my %args = @_;
     if (my $err = $validator->(\%args)) { return $err }


or, if you want to die on validation failure:

 $SPEC{foo} = {
 sub foo {
     state $validator = gen_args_validator(die => 1);
     my %args = @_;


Perinci::Sub::ValidateArgs will retrieve the Rinci metadata from the caller's
C<%SPEC> package variable, then generate Perl validator code for all the
arguments specified in the Rinci metadata, and compose them into a single
arguments validator subroutine which is then returned for you to use. This
generation process is only done once, the first time your function is called.
The subsequent call will be faster since the arguments validator routine is
cached by the state variable. Note that state variable is available from perl
5.010. If you are stuck with older perl, you can use the alternative solution

 my $validator_foo;
 sub foo {
     $validator_foo ||= gen_args_validator();
     if (my $err = $validator_foo->(\%args)) { return $err }

or perhaps:

     my $validator;
     sub foo {
         $validator ||= gen_args_validator();
         if (my $err = $validator->(\%args)) { return $err }

Using Perinci::Sub::ValidateArgs is more convenient than using the dzil plugin
because you do not need to build a Perl distribution first. But this method is a
tiny bit slower during runtime and will require Data::Sah during runtime.

Two other alternatives are available under some situation.

=head2 Perinci::CmdLine::Lite and Perinci::CmdLine::Inline

If you only use your function through a CLI using L<Perinci::CmdLine::Lite> or
L<Perinci::CmdLine::Inline> framework, you can skip validating in the function
body and let the framework validate (or generate a validator) for you.

During runtime, Perinci::CmdLine::Lite will retrieve your function's Rinci
metadata and generate Data::Sah validators for all the specified arguments and
check them. This means you will require Data::Sah during runtime.

Perinci::CmdLine::Inline on the other hand will generate a CLI script with the
arguments validator embedded in it. Data::Sah will no longer be required during

Note that if your Rinci metadata already contains this attribute
C<x.perl.validate_args> set to true, argument validation will not be done.

=head2 Perinci::Sub::Wrapper (used by e.g. Perinci::CmdLine::Classic)

L<Perinci::Sub::Wrapper> will create a wrapper for your function and add
functionalities (including argument validation) according to information from
Rinci metadata. This can be done dynamically, or the wrapper code can be
included in the source code during distribution build time using

L<Perinci::CmdLine::Classic> is a CLI framework which uses Perinci::Sub::Wrapper
to perform argument validation.


TBD. L<Data::Sah::Params>.


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

=head1 SOURCE

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

=head1 BUGS

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

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

=head1 SEE ALSO

Alternatives to L<Sah>/L<Data::Sah> to validate your function/method parameters:
L<Params::Validate>, L<Type::Tiny>/L<Type::Params> (see

=head1 AUTHOR

perlancar <perlancar@cpan.org>


This software is copyright (c) 2021, 2020, 2019, 2018, 2017, 2016, 2015, 2014, 2013, 2012 by 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.