#130 add simple filter tutorial for cpp #239

EsipovPA · 2026-01-03T13:04:33Z

Description

Add a tutorial for using the SimpleFilter class to create new filters.

Adresses #130

Is this user-facing behavior change?

Yes. It is a UX improvement.

Did you use Generative AI?

No, I did not.

Additional Information

fujitatomoya

overall lgtm with minor comments.

@CursedRock17 can you take a look at this?

fujitatomoya · 2026-01-05T02:04:00Z

doc/Tutorials/Chain-Python.rst

 This filter class will be a successor to the ``SimpleFilter`` class, but this is a topic for another tutorial.
-
-.. TODO: @EsipovPA: Add message_filters.SimpleFilter tutorial reference, when ready
+For more information on this topic, please refer to the `SimpleFilter for Python tutorial <https://docs.ros.org/en/jazzy/p/message_filters/doc/Tutorials/SimpleFilter-Python.html>`.


should we point it to the rolling branch? (the same comment goes else where.)

Suggested change

For more information on this topic, please refer to the `SimpleFilter for Python tutorial <https://docs.ros.org/en/jazzy/p/message_filters/doc/Tutorials/SimpleFilter-Python.html>`.

For more information on this topic, please refer to the `SimpleFilter for Python tutorial <https://docs.ros.org/en/rolling/p/message_filters/doc/Tutorials/SimpleFilter-Python.html>`.

Yes I would agree with changing this rolling

Thanks for noticing this. Also, it might be an issue when backporting this to other releases. This should be valid for every release, so it should be changed by hand before merging MRs created by the bot if will be used.

upd

Fixed here in this PR

fujitatomoya · 2026-01-05T02:06:54Z

doc/Tutorials/SimpleFilter-Cpp.rst

+1. Create a Basic Node
+~~~~~~~~~~~~~~~~~~~~~~
+
+Let's assume, you've already created an empty ROS 2 package for C++.


to keep the consistency, probably we would want to quote it? or maybe unquote all of them?

Suggested change

Let's assume, you've already created an empty ROS 2 package for C++.

Let's assume, you've already created an empty ROS 2 package for ``C++``.

ahcorde · 2026-01-07T08:31:19Z

doc/Tutorials/Chain-Python.rst


-.. More on this succession mechanism should be in the corresponding tutorial
-.. TODO: @EsipovPA Add link to the message_filters.SimpleFilter tutorial, when added.
+For more information on this succession mechanism, please refer to the `SimpleFilter for Python tutorial <https://docs.ros.org/en/jazzy/p/message_filters/doc/Tutorials/SimpleFilter-Python.html>`.


Suggested change

For more information on this succession mechanism, please refer to the `SimpleFilter for Python tutorial <https://docs.ros.org/en/jazzy/p/message_filters/doc/Tutorials/SimpleFilter-Python.html>`.

For more information on this succession mechanism, please refer to the `SimpleFilter for Python tutorial <https://docs.ros.org/en/rolling/p/message_filters/doc/Tutorials/SimpleFilter-Python.html>`.

ahcorde · 2026-01-07T08:31:36Z

doc/Tutorials/SimpleFilter-Cpp.rst

+SimpleFilter (C++):
+------------


Suggested change

SimpleFilter (C++):

------------

SimpleFilter (C++):

-------------------

ahcorde · 2026-01-07T08:33:30Z

doc/Tutorials/SimpleFilter-Cpp.rst

+
+	ament_auto_add_executable(simple_filter_tutorial src/simple_filter_tutorial.cpp)
+
+Finally, add the install(TARGETS…) section so ros2 run can find your executable:


Suggested change

Finally, add the install(TARGETS…) section so ros2 run can find your executable:

Finally, add the ``install(TARGETS…)`` section so ros2 run can find your executable:

Fixed here and in another tutorials as well.

ahcorde · 2026-01-07T08:34:13Z

doc/Tutorials/SimpleFilter-Cpp.rst

+.. code-block:: console
+
+[INFO] [1766958211.195602859] [SimpleFilterExampleNode]: No messages published yet
+[INFO] [1766958212.195809044] [SimpleFilterExampleNode]: Published messages count: 1. Last message: Pub count: 1
+[INFO] [1766958213.195618995] [SimpleFilterExampleNode]: Published messages count: 2. Last message: Pub count: 2
+[INFO] [1766958214.195599466] [SimpleFilterExampleNode]: Published messages count: 3. Last message: Pub count: 3
+[INFO] [1766958215.195890964] [SimpleFilterExampleNode]: Published messages count: 4. Last message: Pub count: 4
+[INFO] [1766958216.195910443] [SimpleFilterExampleNode]: Published messages count: 5. Last message: Pub count: 5
+[INFO] [1766958217.195906785] [SimpleFilterExampleNode]: Published messages count: 6. Last message: Pub count: 6
+[INFO] [1766958218.195652168] [SimpleFilterExampleNode]: Published messages count: 7. Last message: Pub count: 7


Suggested change

.. code-block:: console

[INFO] [1766958211.195602859] [SimpleFilterExampleNode]: No messages published yet

[INFO] [1766958212.195809044] [SimpleFilterExampleNode]: Published messages count: 1. Last message: Pub count: 1

[INFO] [1766958213.195618995] [SimpleFilterExampleNode]: Published messages count: 2. Last message: Pub count: 2

[INFO] [1766958214.195599466] [SimpleFilterExampleNode]: Published messages count: 3. Last message: Pub count: 3

[INFO] [1766958215.195890964] [SimpleFilterExampleNode]: Published messages count: 4. Last message: Pub count: 4

[INFO] [1766958216.195910443] [SimpleFilterExampleNode]: Published messages count: 5. Last message: Pub count: 5

[INFO] [1766958217.195906785] [SimpleFilterExampleNode]: Published messages count: 6. Last message: Pub count: 6

[INFO] [1766958218.195652168] [SimpleFilterExampleNode]: Published messages count: 7. Last message: Pub count: 7

.. code-block:: console

[INFO] [1766958211.195602859] [SimpleFilterExampleNode]: No messages published yet

[INFO] [1766958212.195809044] [SimpleFilterExampleNode]: Published messages count: 1. Last message: Pub count: 1

[INFO] [1766958213.195618995] [SimpleFilterExampleNode]: Published messages count: 2. Last message: Pub count: 2

[INFO] [1766958214.195599466] [SimpleFilterExampleNode]: Published messages count: 3. Last message: Pub count: 3

[INFO] [1766958215.195890964] [SimpleFilterExampleNode]: Published messages count: 4. Last message: Pub count: 4

[INFO] [1766958216.195910443] [SimpleFilterExampleNode]: Published messages count: 5. Last message: Pub count: 5

[INFO] [1766958217.195906785] [SimpleFilterExampleNode]: Published messages count: 6. Last message: Pub count: 6

[INFO] [1766958218.195652168] [SimpleFilterExampleNode]: Published messages count: 7. Last message: Pub count: 7

ahcorde · 2026-01-07T08:34:58Z

doc/Tutorials/SimpleFilter-Cpp.rst

+      typedef MessageEvent<M const> EventType;
+
+We start with a few ``typedef declarations`` for ``MConstPtr``, ``Callback`` and ``EventType``.
+These will make the following code clearer and easyer to read.


Suggested change

These will make the following code clearer and easyer to read.

These will make the following code clearer and easier to read.

ahcorde · 2026-01-07T08:35:09Z

doc/Tutorials/SimpleFilter-Cpp.rst

+        );
+      }
+
+In order to create a connection with another filter, this method registeres the ``add`` method of this class


Suggested change

In order to create a connection with another filter, this method registeres the ``add`` method of this class

In order to create a connection with another filter, this method registers the ``add`` method of this class

ahcorde · 2026-01-07T08:35:18Z

doc/Tutorials/SimpleFilter-Cpp.rst

+
+The private section in this case is rather simple.
+It consists of the ``counter_`` and the ``last_message_cache_`` fields and the ``incoming_connection_`` field.
+First two are the part of the buisness logic of this class.


Suggested change

First two are the part of the buisness logic of this class.

First two are the part of the business logic of this class.

ahcorde · 2026-01-07T08:35:26Z

doc/Tutorials/SimpleFilter-Cpp.rst

+[INFO] [1766958217.195906785] [SimpleFilterExampleNode]: Published messages count: 6. Last message: Pub count: 6
+[INFO] [1766958218.195652168] [SimpleFilterExampleNode]: Published messages count: 7. Last message: Pub count: 7
+
+Note that when the first query is executed, there were no messages that have pasesd the filter, as is indicated by the console output.


Suggested change

Note that when the first query is executed, there were no messages that have pasesd the filter, as is indicated by the console output.

Note that when the first query is executed, there were no messages that have passed the filter, as is indicated by the console output.

EsipovPA · 2026-01-07T09:52:59Z

Thank you all for the review.
I'm out of town for a few days and with not that good of an internet connection.

I'll definetely fix the code when I'm back home.

CursedRock17

For the most part LGTM, I just wanted to go through and build the node just to make sure it was followable. Found a slight error in a typo with the main CounterWilthLastMessageCache which has wilth instead of with. Other than that just nitpicking for readability.

Great work!

CursedRock17 · 2026-01-07T04:10:58Z

doc/Tutorials/Chain-Python.rst

 This filter class will be a successor to the ``SimpleFilter`` class, but this is a topic for another tutorial.
-
-.. TODO: @EsipovPA: Add message_filters.SimpleFilter tutorial reference, when ready
+For more information on this topic, please refer to the `SimpleFilter for Python tutorial <https://docs.ros.org/en/jazzy/p/message_filters/doc/Tutorials/SimpleFilter-Python.html>`.


Yes I would agree with changing this rolling

CursedRock17 · 2026-01-07T04:16:38Z

doc/Tutorials/SimpleFilter-Cpp.rst

+    namespace message_filters
+    {
+    template<class M>
+    class CounterWilthLastMessageCache : public SimpleFilter<M> {


Typo on Class

Suggested change

class CounterWilthLastMessageCache : public SimpleFilter<M> {

class CounterWithLastMessageCache : public SimpleFilter<M> {

CursedRock17 · 2026-01-07T04:17:20Z

doc/Tutorials/SimpleFilter-Cpp.rst

+      virtual ~CounterWilthLastMessageCache() {}
+
+      CounterWilthLastMessageCache() {}
+
+      template<typename F>
+      explicit CounterWilthLastMessageCache(F & filter)


Typo continued.

Suggested change

virtual ~CounterWilthLastMessageCache() {}

CounterWilthLastMessageCache() {}

template<typename F>

explicit CounterWilthLastMessageCache(F & filter)

virtual ~CounterWithLastMessageCache() {}

CounterWithLastMessageCache() {}

template<typename F>

explicit CounterWithLastMessageCache(F & filter)

It was a typo in a first class declaration in the actual project where I've tested the code, and after that is was autocompletion in vscode. Should always remind myself not to trust autocompletion completely (this one is intended) 🤦‍♂️

CursedRock17 · 2026-01-07T04:17:32Z

doc/Tutorials/SimpleFilter-Cpp.rst

+        incoming_connection_ = filter.registerCallback(
+          typename SimpleFilter<M>::EventCallback(
+            std::bind(
+              &CounterWilthLastMessageCache::add,


Suggested change

&CounterWilthLastMessageCache::add,

&CounterWithLastMessageCache::add,

CursedRock17 · 2026-01-07T04:20:53Z

doc/Tutorials/SimpleFilter-Cpp.rst

+This tutorial demonstrates how to create a custom filter that is going to be a successor to the ``SimpleFilter`` class.
+The ``SimpleFilter`` is a base class for almost all of message filters implemented in ``C++``.
+It provides the basic functionality for building filters.
+To demonstrate the functionality of this filter we are going to create a ``CounterWilthLastMessageCache`` filter class.


Small Typo.

Suggested change

To demonstrate the functionality of this filter we are going to create a ``CounterWilthLastMessageCache`` filter class.

To demonstrate the functionality of this filter we are going to create a ``CounterWithLastMessageCache`` filter class.

CursedRock17 · 2026-01-08T06:18:20Z

doc/Tutorials/SimpleFilter-Cpp.rst

+The private section in this case is rather simple.
+It consists of the ``counter_`` and the ``last_message_cache_`` fields and the ``incoming_connection_`` field.
+First two are the part of the buisness logic of this class.
+The last one is required for managing the connection with a filter that does pass messages to this one.


Suggested change

The last one is required for managing the connection with a filter that does pass messages to this one.

The last one manages the connection with a filter that passes messages to this one.

CursedRock17 · 2026-01-08T06:22:12Z

doc/Tutorials/SimpleFilter-Cpp.rst

+The instance of the ``SubscriberFilter``is used to receive messages from the ``TUTORIAL_TOPIC``.
+The instance of the ``CounterWilthLastMessageCache`` filter is immediately connected to the ``subscriber_filter_``'s output.


Inline code block breaking up and typo change.

Suggested change

The instance of the ``SubscriberFilter``is used to receive messages from the ``TUTORIAL_TOPIC``.

The instance of the ``CounterWilthLastMessageCache`` filter is immediately connected to the ``subscriber_filter_``'s output.

The instance of the ``SubscriberFilter`` receives messages from the ``TUTORIAL_TOPIC``.

The instance of the ``CounterWithLastMessageCache`` filter is immediately connected to the ``subscriber_filter_``'s output.

CursedRock17 · 2026-01-08T06:23:55Z

doc/Tutorials/SimpleFilter-Cpp.rst

+And the two timers are added to automate the work.
+The ``publisher_timer_`` to automate message publishing.
+And the ``query_timer_`` to automate the introspection of the node filters state.


Breaking up the section

Suggested change

And the two timers are added to automate the work.

The ``publisher_timer_`` to automate message publishing.

And the ``query_timer_`` to automate the introspection of the node filters state.

Two timers are added to automate the work:

The ``publisher_timer_`` automates message publishing.

The ``query_timer_`` automates the introspection of the node filter's state.

CursedRock17 · 2026-01-08T06:29:28Z

doc/Tutorials/SimpleFilter-Cpp.rst

+        incoming_connection_ = filter.registerCallback(
+          typename SimpleFilter<M>::EventCallback(
+            std::bind(
+              &CounterWilthLastMessageCache::add,


Typo continued.

Suggested change

&CounterWilthLastMessageCache::add,

&CounterWithLastMessageCache::add,

CursedRock17 · 2026-01-08T06:29:55Z

doc/Tutorials/SimpleFilter-Cpp.rst

+
+    private:
+      message_filters::Subscriber<std_msgs::msg::String> subscriber_filter_;
+      message_filters::CounterWilthLastMessageCache<std_msgs::msg::String> counter_filter_;


Typo Continued.

Suggested change

message_filters::CounterWilthLastMessageCache<std_msgs::msg::String> counter_filter_;

message_filters::CounterWithLastMessageCache<std_msgs::msg::String> counter_filter_;

…ference. Fix minor typos in Chain and Cache tutorials Signed-off-by: EsipovPA <esipov.p@mail.ru>

Signed-off-by: EsipovPA <esipov.p@mail.ru>

ahcorde · 2026-01-12T08:41:02Z

Pulls: #239
Gist: https://gist.githubusercontent.com/ahcorde/876b4e0cbc45e2c50fb341b16729bf14/raw/bffcf0b08eed6bfb9507ec43d57498314d6678f0/ros2.repos
BUILD args: --packages-above-and-dependencies message_filters
TEST args: --packages-above message_filters
ROS Distro: rolling
Job: ci_launcher
ci_launcher ran: https://ci.ros2.org/job/ci_launcher/17909

Linux
Linux-aarch64
Linux-rhel
Windows

EsipovPA · 2026-01-12T18:43:44Z

Hello @ahcorde! Thanks for the review and for the approval. It seems like the 'Linux' job is not running. It was in a 'failing' state for some time, but now it is just in 'not run'. Is there anything to be done about it? Maybe there is something, I can do? Sorry for bothering, if I'm being inconvenient.

ahcorde · 2026-01-13T11:35:41Z

https://github.com/Mergifyio backport kilted jazzy humble

mergify · 2026-01-13T11:35:58Z

backport kilted jazzy humble

✅ Backports have been created

Details

#240 #130 add simple filter tutorial for cpp (backport #239) has been created for branch kilted
#241 #130 add simple filter tutorial for cpp (backport #239) has been created for branch jazzy
#242 #130 add simple filter tutorial for cpp (backport #239) has been created for branch humble

Signed-off-by: EsipovPA <esipov.p@mail.ru> (cherry picked from commit 92af2b7)

* #130 add simple filter tutorial for cpp (#239) Signed-off-by: EsipovPA <esipov.p@mail.ru> (cherry picked from commit 92af2b7) Signed-off-by: Alejandro Hernandez Cordero <ahcorde@gmail.com> Co-authored-by: Pavel Esipov <38457822+EsipovPA@users.noreply.github.com> Co-authored-by: Alejandro Hernandez Cordero <ahcorde@gmail.com>

fujitatomoya reviewed Jan 5, 2026

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ahcorde requested changes Jan 7, 2026

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CursedRock17 suggested changes Jan 8, 2026

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EsipovPA added 2 commits January 10, 2026 00:52

(ros2#130) Chain (Python): Resolve TODO. Add SimpleFilter tutorial re…

ca07c51

…ference. Fix minor typos in Chain and Cache tutorials Signed-off-by: EsipovPA <esipov.p@mail.ru>

(ros2#130) SimpleFilter (C++): Add SimpleFilter tutorial for C++

6459e47

Signed-off-by: EsipovPA <esipov.p@mail.ru>

EsipovPA force-pushed the 130_add_simple_filter_tutorial_for_cpp branch from 4c6021e to 6459e47 Compare January 9, 2026 21:53

ahcorde approved these changes Jan 12, 2026

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EsipovPA requested a review from CursedRock17 January 12, 2026 15:44

CursedRock17 approved these changes Jan 13, 2026

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ahcorde merged commit 92af2b7 into ros2:rolling Jan 13, 2026
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mergify bot pushed a commit that referenced this pull request Jan 13, 2026

#130 add simple filter tutorial for cpp (#239)

d188c31

Signed-off-by: EsipovPA <esipov.p@mail.ru> (cherry picked from commit 92af2b7)

mergify bot mentioned this pull request Jan 13, 2026

#130 add simple filter tutorial for cpp (backport #239) #240

Merged

mergify bot pushed a commit that referenced this pull request Jan 13, 2026

#130 add simple filter tutorial for cpp (#239)

78ec120

Signed-off-by: EsipovPA <esipov.p@mail.ru> (cherry picked from commit 92af2b7)

mergify bot pushed a commit that referenced this pull request Jan 13, 2026

#130 add simple filter tutorial for cpp (#239)

b1ef59b

Signed-off-by: EsipovPA <esipov.p@mail.ru> (cherry picked from commit 92af2b7)

This was referenced Jan 13, 2026

#130 add simple filter tutorial for cpp (backport #239) #241

Merged

#130 add simple filter tutorial for cpp (backport #239) #242

Merged

	For more information on this topic, please refer to the `SimpleFilter for Python tutorial <https://docs.ros.org/en/jazzy/p/message_filters/doc/Tutorials/SimpleFilter-Python.html>`.
	For more information on this topic, please refer to the `SimpleFilter for Python tutorial <https://docs.ros.org/en/rolling/p/message_filters/doc/Tutorials/SimpleFilter-Python.html>`.

	Let's assume, you've already created an empty ROS 2 package for C++.
	Let's assume, you've already created an empty ROS 2 package for ``C++``.

	For more information on this succession mechanism, please refer to the `SimpleFilter for Python tutorial <https://docs.ros.org/en/jazzy/p/message_filters/doc/Tutorials/SimpleFilter-Python.html>`.
	For more information on this succession mechanism, please refer to the `SimpleFilter for Python tutorial <https://docs.ros.org/en/rolling/p/message_filters/doc/Tutorials/SimpleFilter-Python.html>`.


		ament_auto_add_executable(simple_filter_tutorial src/simple_filter_tutorial.cpp)

		Finally, add the install(TARGETS…) section so ros2 run can find your executable:

	Finally, add the install(TARGETS…) section so ros2 run can find your executable:
	Finally, add the ``install(TARGETS…)`` section so ros2 run can find your executable:

	These will make the following code clearer and easyer to read.
	These will make the following code clearer and easier to read.

	In order to create a connection with another filter, this method registeres the ``add`` method of this class
	In order to create a connection with another filter, this method registers the ``add`` method of this class

	First two are the part of the buisness logic of this class.
	First two are the part of the business logic of this class.

	Note that when the first query is executed, there were no messages that have pasesd the filter, as is indicated by the console output.
	Note that when the first query is executed, there were no messages that have passed the filter, as is indicated by the console output.

	class CounterWilthLastMessageCache : public SimpleFilter<M> {
	class CounterWithLastMessageCache : public SimpleFilter<M> {

	&CounterWilthLastMessageCache::add,
	&CounterWithLastMessageCache::add,

	To demonstrate the functionality of this filter we are going to create a ``CounterWilthLastMessageCache`` filter class.
	To demonstrate the functionality of this filter we are going to create a ``CounterWithLastMessageCache`` filter class.

	The last one is required for managing the connection with a filter that does pass messages to this one.
	The last one manages the connection with a filter that passes messages to this one.

		The instance of the ``SubscriberFilter``is used to receive messages from the ``TUTORIAL_TOPIC``.
		The instance of the ``CounterWilthLastMessageCache`` filter is immediately connected to the ``subscriber_filter_``'s output.

	message_filters::CounterWilthLastMessageCache<std_msgs::msg::String> counter_filter_;
	message_filters::CounterWithLastMessageCache<std_msgs::msg::String> counter_filter_;

#130 add simple filter tutorial for cpp #239

#130 add simple filter tutorial for cpp #239

Conversation

EsipovPA commented Jan 3, 2026

Description

Is this user-facing behavior change?

Did you use Generative AI?

Additional Information

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EsipovPA commented Jan 7, 2026

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