{
   package Page;

   use strict;
   use warnings;

   use Moose;

   has 'url' => (
      is       => 'ro',
      isa      => 'Str',
      required => 1,
   );


   use Moose::Util::TypeConstraints;

   subtype 'Pages'
      => as 'ArrayRef[Page]';

   coerce 'Pages'
      => from 'ArrayRef[HashRef]'
         => via { [ map __PACKAGE__->new($_), @{ $_[0] } ] };

   no Moose::Util::TypeConstraints;


   no Moose;
   __PACKAGE__->meta->make_immutable();
}

{
   package Container;

   use strict;
   use warnings;

   use Moose;

   has 'pages' => (
      is      => 'rw',
      isa     => 'Pages',
      coerce  => 1,
      default => sub { [ ] },
   );

   no Moose;
   __PACKAGE__->meta->make_immutable();
}

Container->new( pages => [ { url => "a" }, { url => "b" } ] );
[download]

I don't really like the global-ness of the coercion. I'll be posting an alternative that uses BUILDARGS shortly.