On 06/02/17 15:51, Chapman Flack wrote:
> But what it buys you is then if your MyExtraPGNode has PostgresNode
> as a base, the familiar idiom
>   MyExtraPGNode->get_new_node('foo');
> works, as it inserts the class as the first argument.
> As a bonus, you then don't need to complicate get_new_node
> with a test for (not ($node->isa("PostgresNode"))) because
> if it weren't, it wouldn't have inherited get_new_node

Any takers if I propose this amendment in the form of a patch?

Relying on the perl idiom instead of a $node->isa() test shortens
the patch; does that ameliorate at all the concern about complicating
core for the benefit of modules?

I'm not fully persuaded that just re-blessing a PostgresNode suffices
as a workaround ... if the subclass expects to have additional state
set up by its own constructor, the deception seems likely to be exposed.
So I think there are more than just cosmetic grounds for allowing this.

--- src/test/perl/PostgresNode.pm	2017-06-07 20:15:52.827639829 -0400
+++ src/test/perl/PostgresNode.pm	2017-06-07 20:57:49.205145761 -0400
@@ -853,20 +853,27 @@
-=item get_new_node(node_name)
+=item get_new_node(node_name) I<or> PostgresNode->get_new_node(node_name)
-Build a new PostgresNode object, assigning a free port number. Standalone
-function that's automatically imported.
+Build a new PostgresNode object, assigning a free port number. This can be
+called either as a standalone function that's automatically imported, or as
+a class method on PostgresNode or any subclass.
 Remembers the node, to prevent its port number from being reused for another
 node, and to ensure that it gets shut down when the test script exits.
 You should generally use this instead of PostgresNode::new(...).
+If you have a subclass of PostgresNode you want created, use the class-method
+form of the call, as in C<MyExtendedPostgresNode->get_new_node(node_name)>.
+The standalone-function form creates an instance of PostgresNode.
 sub get_new_node
+	my $class = 'PostgresNode';
+	$class = shift if 1 < scalar @_;
 	my $name  = shift;
 	my $found = 0;
 	my $port  = $last_port_assigned;
@@ -911,7 +918,7 @@
 	print "# Found free port $port\n";
 	# Lock port number found by creating a new node
-	my $node = new PostgresNode($name, $test_pghost, $port);
+	my $node = $class->new($name, $test_pghost, $port);
 	# Add node to list of nodes
 	push(@all_nodes, $node);
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