Beefy Boxes and Bandwidth Generously Provided by pair Networks
Clear questions and runnable code
get the best and fastest answer

comment on

( #3333=superdoc: print w/replies, xml ) Need Help??

Whereas C++ and Java go to great lengths to ensure that the data types of any arguments passed to a function, match what is expected, perl is often criticised for not enforcing anything.

Perl 6 will address this issue, but in the mean time, any subroutines you write are passed an array @_ containing a potential hotch-potch of scalars and references, blessed or otherwise.

Although it's nice to write code that can DWIM given a parameter of varying data types, this is always an extra effort to implement. Also, what will your sub do when passed a SCALAR when it's expecting an ARRAYREF? At best, it will die with a run-time error, and a message which likely as not, would not be immediately obvious.

Enter Params::Validate

By default, this module exports the functions validate and validate_pos. Params::Validate caters for two calling conventions: named parameters and positional parameters, which are validated by validate and validate_pos respectively. Unfortunately you can't mix them; any positional parameters before your list of key/value pairs need to be removed first. In fact, this is the way to use Params::Validate to handle method calls. Examples:
sub mymethod { my $self = shift; my %args = validate( @_, { foo => 1, bar => { default => 99} } ); ... } sub mymethod2 { my $self = shift; my ($meenie,$minie,$mo) = validate_pos( @_, { type => SCALAR }, { type => SCALAR | UNDEF }, { type => ARRAYREF, default => [] } ); ... }
As is apparent, the call to validate or validate_pos is quite straightforward and edifying to someone else looking at the code.

It's also quite easy to add such validation to existing code, for an immediate gain in robustness without too much cognitive effort. The module provides a whole host of tools for validating your argument list - I have just scratched the surface.

Error handling

When the parameter validation fails, the default action it to croak, with quite a helpful message about which parameter is invalid and why. You can elect to use a callback to catch validation errors instead.


I am a convert to using this module. I recommend it for CPAN modules and for corporate coding standards.


I have had some interesting dependency issues with modules of mine that are using Params::Validate. I have seen CPAN pull in Ponie via Attribute::Handlers. Why would I want the Parrot/Ponie stuff coming into my production environment ?! I asked Arthur Bergman about this, and apparently it is a spurious dependency picked up by, apparently sorted in a later release of Attribute::Handlers.

I did notice also that ActiveState's module status page was showing any of my modules that use Params::Validate, as having a dependency on Ponie.

In reply to Params::Validate by rinceWind

Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post; it's "PerlMonks-approved HTML":

  • Are you posting in the right place? Check out Where do I post X? to know for sure.
  • Posts may use any of the Perl Monks Approved HTML tags. Currently these include the following:
    <code> <a> <b> <big> <blockquote> <br /> <dd> <dl> <dt> <em> <font> <h1> <h2> <h3> <h4> <h5> <h6> <hr /> <i> <li> <nbsp> <ol> <p> <small> <strike> <strong> <sub> <sup> <table> <td> <th> <tr> <tt> <u> <ul>
  • Snippets of code should be wrapped in <code> tags not <pre> tags. In fact, <pre> tags should generally be avoided. If they must be used, extreme care should be taken to ensure that their contents do not have long lines (<70 chars), in order to prevent horizontal scrolling (and possible janitor intervention).
  • Want more info? How to link or How to display code and escape characters are good places to start.
Log In?

What's my password?
Create A New User
Domain Nodelet?
and the web crawler heard nothing...

How do I use this? | Other CB clients
Other Users?
Others scrutinizing the Monastery: (5)
As of 2023-06-05 13:23 GMT
Find Nodes?
    Voting Booth?
    How often do you go to conferences?

    Results (24 votes). Check out past polls.