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three minor comments...
  • Why make the mutators "set_foo" ... why not just overload "foo" (ie: foo with args does a set, and returns true if-and-only-if the args are valid, without args returns whatever the parameter value(s) should be.
  • Frequently when I've needed to use Parameter Objects (or "Keys" as their sometimes called) there are acctually two issues of validity:
    1. Are the individual parameters valid?
    2. is the combination of parameters valid?
    ... you've addressed the first, but not the second. There are lots of examples of when this becomes crucial, but the the most basic is: what if none of the set methods are called?" Typically the easiest solution is to have a unified "isValid" method on all of your Parameter Objects that returns true if-and-only-if all of the required parameters have been set, and there is "internal consistency" among the parameters, then any method that wants to take in a Parameter object doesn't need to do it's own validation, it can just call $param->isValid() However ... in cases where i've seen this done, it works becaue the methods expect a particular sub class of the "Parameter Object" class, and each sub class defines it's own isValid method. Based on your design, I'm not really sure what the best way to do this would be (because whoever calls "new Sub::ParamObject" can pass whatever rules they want.
  • Your example validation for month has a slight bug in it...
    my %params = ( type => qr/Order|Return/, month => sub { my $month = shift; return grep { /$month/ } (1 .. 1 +2) } );
    ..that would allow me to pass '' as a valid month.

In reply to Re: RFC - Parameter Objects by hossman
in thread RFC - Parameter Objects by Ovid

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