Author image Robert 'phaylon' Sedlacek
and 1 contributors


Declare::Constraints::Simple::Library::Hash - Hash Constraints


  my $constraint = And(

    # make sure all keys are present
    HasAllKeys( qw(foo bar) ),

    # constraints for the keys
    OnHashKeys( foo => IsInt, bar => HasLength )



This module contains all constraints that can be applied to hash references.


The value has to be a hashref, and contain all keys listed in @keys to pass this constraint.

The stack or path part of HasAllKeys is HasAllKeys[$key] where $key is the missing key.

OnHashKeys(key => $constraint, key => $constraint, ...)

This allows you to pass a constraint for each specific key in a hash reference. If a specified key is not in the validated hash reference, the validation for this key is not done. To make a key a requirement, use HasAllKeys(@keys) above in combination with this, e.g. like:

  And( HasAllKeys( qw(foo bar baz) )
       OnHashKeys( foo => IsInt,
                   bar => Matches(qr/bar/),
                   baz => IsArrayRef( HasLength )));

Also, as you might see, you don't have to check for IsHashRef validity here. The hash constraints are already doing that by themselves.

The stack or path part of OnHashKeys looks like OnHashKeys[$key] where $key is the key of the failing value.


Declare::Constraints::Simple, Declare::Constraints::Simple::Library


Robert 'phaylon' Sedlacek <>


This module is free software, you can redistribute it and/or modify it under the same terms as perl itself.