remove need for instance() call

bin/netdisco-do

@@ -138,7 +138,7 @@ unless ($action) {
         $extra = $class;
         undef $class;
     }
-    my $i = App::Netdisco::Core::Transport::SNMP->instance->reader_for($device, $class);
+    my $i = App::Netdisco::Core::Transport::SNMP->reader_for($device, $class);
     Data::Printer::p($i->$extra);
     return ('done', sprintf "Showed %s response from %s.", $extra, $device->ip);
   }

lib/App/Netdisco/Backend/Worker/Interactive/DeviceActions.pm

@@ -22,7 +22,7 @@ sub _set_device_generic {
   $data ||= '';
 
   # snmp connect using rw community
-  my $info = App::Netdisco::Core::Transport::SNMP->instance->writer_for($ip)
+  my $info = App::Netdisco::Core::Transport::SNMP->writer_for($ip)
     or return job_defer("Failed to connect to device [$ip] to update $slot");
 
   my $method = 'set_'. $slot;

lib/App/Netdisco/Backend/Worker/Interactive/PortActions.pm

@@ -74,7 +74,7 @@ sub _set_port_generic {
 
   if ($device->vendor ne 'netdisco') {
       # snmp connect using rw community
-      my $info = App::Netdisco::Core::Transport::SNMP->instance->writer_for($ip)
+      my $info = App::Netdisco::Core::Transport::SNMP->writer_for($ip)
         or return job_defer("Failed to connect to device [$ip] to control port");
 
       my $iid = get_iid($info, $port)
@@ -127,7 +127,7 @@ sub power {
   $data = 'false' if $data =~ m/^(off|no|down)$/;
 
   # snmp connect using rw community
-  my $info = App::Netdisco::Core::Transport::SNMP->instance->writer_for($ip)
+  my $info = App::Netdisco::Core::Transport::SNMP->writer_for($ip)
     or return job_defer("Failed to connect to device [$ip] to control power");
 
   my $powerid = get_powerid($info, $port)

lib/App/Netdisco/Backend/Worker/Poller/Common.pm

@@ -63,7 +63,7 @@ sub _single_body {
       return job_defer("$job_type deferred: $host is not ${job_type}able");
   }
 
-  my $snmp = App::Netdisco::Core::Transport::SNMP->instance->reader_for($device);
+  my $snmp = App::Netdisco::Core::Transport::SNMP->reader_for($device);
   if (!defined $snmp) {
       return job_defer("$job_type failed: could not SNMP connect to $host");
   }

lib/App/Netdisco/Backend/Worker/Poller/Device.pm

@@ -59,7 +59,7 @@ sub discover {
       return job_defer("discover deferred: $host is not discoverable");
   }
 
-  my $snmp = App::Netdisco::Core::Transport::SNMP->instance->reader_for($device);
+  my $snmp = App::Netdisco::Core::Transport::SNMP->reader_for($device);
   if (!defined $snmp) {
       return job_defer("discover failed: could not SNMP connect to $host");
   }

lib/App/Netdisco/Core/Transport/SNMP.pm

@@ -19,9 +19,9 @@ App::Netdisco::Core::Transport::SNMP
 =head1 DESCRIPTION
 
 Singleton for SNMP connections. Returns cached L<SNMP::Info> instance for a
-given device IP, or else undef. Prefix calls to this class with:
+given device IP, or else undef. All methods are class methods, for example:
 
- App::Netdisco::Core::Transport::SNMP->instance()
+ App::Netdisco::Core::Transport::SNMP->reader_for( ... );
 
 =cut
 
@@ -41,8 +41,8 @@ connected to that device. The IP can be any on the device, and the management
 interface will be connected to.
 
 If the device is known to Netdisco and there is a cached SNMP community
-string, this will be tried first, and then other community string(s) from the
+string, that community will be tried first, and then other community strings
-application configuration will be tried.
+from the application configuration will be tried.
 
 If C<$useclass> is provided, it will be used as the L<SNMP::Info> device
 class instead of the class in the Netdisco database.
@@ -52,18 +52,18 @@ Returns C<undef> if the connection fails.
 =cut
 
 sub reader_for {
-  my ($self, $ip, $useclass) = @_;
+  my ($class, $ip, $useclass) = @_;
   my $device = get_device($ip) or return undef;
-  return $self->readers->{$device->ip}
+  my $readers = $class->instance->readers or return undef;
-    if exists $self->readers->{$device->ip};
+  return $readers->{$device->ip} if exists $readers->{$device->ip};
   debug sprintf 'snmp reader cache warm: [%s]', $device->ip;
-  return ($self->readers->{$device->ip}
+  return ($readers->{$device->ip}
     = _snmp_connect_generic('read', $device, $useclass));
 }
 
-=head2 writer_for( $ip, $useclass? )
+=head1 writer_for( $ip, $useclass? )
 
-Same as C<reader_for> but uses the read-write community string(s) from the
+Same as C<reader_for> but uses the read-write community strings from the
 application configuration file.
 
 Returns C<undef> if the connection fails.
@@ -71,16 +71,15 @@ Returns C<undef> if the connection fails.
 =cut
 
 sub writer_for {
-  my ($self, $ip, $useclass) = @_;
+  my ($class, $ip, $useclass) = @_;
   my $device = get_device($ip) or return undef;
-  return $self->writers->{$device->ip}
+  my $writers = $class->instance->writers or return undef;
-    if exists $self->writers->{$device->ip};
+  return $writers->{$device->ip} if exists $writers->{$device->ip};
   debug sprintf 'snmp writer cache warm: [%s]', $device->ip;
-  return ($self->writers->{$device->ip}
+  return ($writers->{$device->ip}
     = _snmp_connect_generic('write', $device, $useclass));
 }
 
-
 sub _snmp_connect_generic {
   my ($mode, $device, $useclass) = @_;
   $mode ||= 'read';