Question

If I have a method that takes either one or the other of two named parameters, exactly one of which must be present, is there a way to handle that with Params::Validate?

  $store->put( content_ref => $stringref );

or

  $store->put( path => $path_to_file );

I’m not seeing it in the docs, but it seems like an obvious use case, so I thought I should ask.

Answer 1

You can use callbacks to achieve something along those lines:

#!/usr/bin/env perl

use strict;
use warnings;

package My::Class;

use Params::Validate;
use YAML;

sub new { bless {} => shift }

sub _xor_param {
    my $param = shift;
    return sub { defined($_[0]) and not defined($_[1]->{$param}) }
}

my %validation_spec = (
    content_ref => {
        'default' => undef,
        callbacks => {
            "Provided only if no 'path' is given"
                => _xor_param('path')
        },
    },
    path => {
        'default' => undef,
        callbacks => {
            "Provided only if no 'content_ref' is given"
                => _xor_param('content_ref')
        },
    },
);

sub put {
    my $self = shift;
    validate(@_, \%validation_spec);
    print Dump \@_;
}

package main;

my $x = My::Class->new;

$x->put(path => 'some path');
$x->put(content_ref => \'some content');
$x->put(path => 'another_path', content_ref => \'some other content');

Output:

---
- path
- some path
---
- content_ref
- !!perl/ref
  =: some content
The 'content_ref' parameter ("SCALAR(0xab83cc)") to My::Class::put did not pass
the 'Provided only if no 'path' is given' callback
 at C:\temp\v.pl line 37
        My::Class::put(undef, 'path', 'another_path', 'content_ref', 
'SCALAR(0xab83cc)') called at C:\temp\v.pl line 47