Mark Jason Dominus gave a talk about the life and death of pseudohashes. (I’d heard of them but had no idea what they actually were before seeing this video.)

I infer from it that fields.pm originated as a convenient interface for pseudohashes and that after they went away fields.pm was kept around mainly for backwards compatibility and reworked to use restricted hashes.

I’d never played with fields.pm before, but I spent a few minutes with it just now and I can guess why it’s not very popular: it doesn't make much of an object. It doesn’t auto-generate accessors or a constructor. (Code is pasted below.) The attempted method call $blurple->blue blows up because there's no blue method. Also, the copy of %params into %{$self} will blow up if you pass any parameter name other than "red", "green", or "blue".

#!/usr/bin/perl

package RGBColor {
    use fields qw(red green blue);

    sub new {
        my RGBColor $self = shift;
        my %params = @_;

        unless (ref $self) {
            $self = fields::new($self);
        }

        %{$self} = %params;
        return $self;
    }
}

my $blurple = RGBColor->new(red => 75, blue => 200, green => 0);

print "blurple's blue is $blurple->{blue}\n";
print "blurple's blue is " . $blurple->blue ."\n";  # kaboom, no such 
+method
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