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<div class="moz-cite-prefix">On 29/05/2023 00:20, Rel wrote:<br>
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<blockquote type="cite" cite="mid:KoULLvq-lcksAeZUuITt4VOATBQrUYwZQqiOzEPTk_DxQRv558HZmIo17DvpAWEU10_jpTqLOCElo8QHRnI8hytgUOKhHRZAcwhmrP4KbOo=@proton.me">
<span>dynamic dispatch</span>
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<div><span>I tried following example [<a target="_blank" rel="noreferrer nofollow noopener" href="https://urldefense.com/v3/__https://github.com/enatai/panamaexperiments/blob/main/libcppexperiments/src/main/public/happy.hpp__;!!ACWV5N9M2RV99hQ!JnMeRRKWI0A8qpGkiXzcR0f06AAFEP-dXJV8lT-ZAMcxwE3BhDeGj91EgKkeMudSckPxr_-N9AlNWSGCtyvUZL0$" moz-do-not-send="true">https://github.com/enatai/panamaexperiments/blob/main/libcppexperiments/src/main/public/happy.hpp</a>]
and it works fine as long as we generate proper Java bindings.</span></div>
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<div><span>See test for it [<a target="_blank" rel="noreferrer
nofollow noopener" href="https://urldefense.com/v3/__https://github.com/enatai/panamaexperiments/blob/main/cppexperiments/src/test/java/cppexperiments/HappyTests.java*L36__;Iw!!ACWV5N9M2RV99hQ!JnMeRRKWI0A8qpGkiXzcR0f06AAFEP-dXJV8lT-ZAMcxwE3BhDeGj91EgKkeMudSckPxr_-N9AlNWSGCRH2ufOA$" moz-do-not-send="true">https://github.com/enatai/panamaexperiments/blob/main/cppexperiments/src/test/java/cppexperiments/HappyTests.java#L36</a>]</span></div>
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<div><span>Please let me know which dynamic dispatch use cases you
are concerned with. Because this one seems works fine.</span></div>
</blockquote>
<p>Sorry, I can see that working fine because you declare a "static"
function which accepts a point, so the vtable indirection is
generated by the CPP compiler in that function.</p>
<p>What I'm worried about is calling virtual methods on classes.
E.g. calling your "distance" function directly. Jextract gives you
two possibilities: Point2d::distance and Point3d::distance. If you
pass a Point3d object to Point2d::distance you will "only" get
Point2d::distance to be called (as if there was no dynamic
dispatch).<br>
</p>
<p><br>
</p>
<blockquote type="cite" cite="mid:KoULLvq-lcksAeZUuITt4VOATBQrUYwZQqiOzEPTk_DxQRv558HZmIo17DvpAWEU10_jpTqLOCElo8QHRnI8hytgUOKhHRZAcwhmrP4KbOo=@proton.me">
<div><br>
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<div><span>std::string</span></div>
<div><span>I totally forgot that such basic type like std::string
in C++ is a template. </span></div>
<div><span>But it seems possible to call functions which operate
with string objects because symbols for them are present:</span></div>
<div><br>
</div>
<div><span>00000000000013ad T _ZN7unhappy10helloWorldB5cxx11Ev</span></div>
<div><br>
</div>
<div><span>std::string helloWorld();</span></div>
<div><br>
</div>
<div><span>I guess it is possible to create/extract layout for
std::string using FFM but:</span></div>
<div><span>- how to initialize this layout from Java? we cannot
just call std::string constructor for it, right?</span></div>
<div><span>- this layout may differ between different C++ runtimes
(libstdc++ etc). MS C++ may have not same std::string layout
as GCC</span></div>
</blockquote>
<p>On the latter, e.g. layout difference, this is no different than
anything else with jextract. E.g. each jextract run is
platform-dependent, as it pulls in header files that are heavily
influenced by the platform and OS you run on.</p>
<p>If I understand correctly, "string" is the "instantiation" of a
template in C++. (e.g. some basic_string<char>). That
instantiation is fully defined (e.g. not partial), and I believe
it should be possible, with libclang, to obtain more information
about it - such as the layout etc. (for partial template
instantiation, my understanding, reading on what Rust bindgen does
is that it is not possible to handle them with libclang).</p>
<p>So, ideally, we should be able to construct a layout for
basic_string<char>, and then pass that to the constructor,
yes.</p>
<p>Maurizio<br>
</p>
<p><br>
</p>
<blockquote type="cite" cite="mid:KoULLvq-lcksAeZUuITt4VOATBQrUYwZQqiOzEPTk_DxQRv558HZmIo17DvpAWEU10_jpTqLOCElo8QHRnI8hytgUOKhHRZAcwhmrP4KbOo=@proton.me">
<div><br>
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<div><span>> Their binding generator adopts the same simple
approach as the one I showed in the patch.</span></div>
<div><br>
</div>
<div><span>I will take a look</span></div>
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<span></span>
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<div class="protonmail_quote"> ------- Original Message -------<br>
On Tuesday, May 23rd, 2023 at 8:58 AM, Maurizio Cimadamore
<a class="moz-txt-link-rfc2396E" href="mailto:maurizio.cimadamore@oracle.com"><maurizio.cimadamore@oracle.com></a> wrote:<br>
<br>
<blockquote class="protonmail_quote" type="cite">
<p><br>
</p>
<div class="moz-cite-prefix">On 23/05/2023 05:11, Rel wrote:<br>
</div>
<blockquote type="cite"> <span>> What I meant for "robust
analysis" was to try and establish how many _real-world_
C++ library can really be tackled in such a direct
approach. </span>
<div><br>
</div>
<div><span>Ohh I see now, I am affraid we know the answer
for this :)</span></div>
<div><br>
</div>
<div><span>Let's imagine if number of C++ libraries which
can be covered end-to-end with "simple" approach is 0,
does it mean that we should discard it and only focus on
shim for binding all kinds of APIs? What about those
cases which can be easily extracted using "simple"
approach, like Point2d?</span></div>
</blockquote>
Perhaps we should reach out to the Rust community? Their
binding generator adopts the same simple approach as the one I
showed in the patch. Given how hard it is to support C++
(because the underlying libclang C API is not very solid in
that respect), I'd be surprised if they maintained all the
necessary code just for stuff like Point2d?<br>
<blockquote type="cite">
<div><br>
</div>
<div><span>Because I thought that we would like to do
"analysis" of what C++ use cases can/cannot be covered
with "simple" approach. For example from your previous
message I see that we are not completely sure about
exceptions:</span></div>
<div><br>
</div>
<div><span>> * (probably way more stuff, like exceptions,
etc.)</span></div>
<div><br>
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<div><span>Similarly for myself I would like to see what are
the problems with "dynamic dispatch". I added it to
"unhappy" for now, because we expect it not to work, but
I plan to test it to see what are the issues there and
share here. Similarly with that anyone would be able to
reproduce and see same results.</span></div>
<div><br>
</div>
<div><span>I guess my question now is: do we think it may be
useful to know exactly how many C++ use cases can be
covered with "simple" FFM approach. And if answer is
yes, then we can use panamaexperiments as a playground
where we can have tests for what is covered. This
(possibly?) can give us more confidence in limitations
of "simple" approach and how far we can go with it (and
this can be easily demonstrated to everyone just by
running those tests)<br>
</span></div>
</blockquote>
<p>I think it would be useful to know some answer to that
question, yes. My intuition tells me that there are probably
two kinds of C++ libraries: those who were born that way,
and those that moved over from being simpler C libraries.
One such example in the latter category is OpenCV [1]. While
its "core" header [2] declares an exception, as well as a
bunch of classes, eyeballing it, it doesn't seem "too"
problematic? Perhaps that would be a good point where to
start, and, if a library such as that can be used with some
degree of success, perhaps we can expand the search to other
similar libraries.</p>
<p>[1] - <a href="https://urldefense.com/v3/__https://opencv.org/__;!!ACWV5N9M2RV99hQ!JnMeRRKWI0A8qpGkiXzcR0f06AAFEP-dXJV8lT-ZAMcxwE3BhDeGj91EgKkeMudSckPxr_-N9AlNWSGC3X8vPfk$" class="moz-txt-link-freetext" rel="noreferrer nofollow
noopener" target="_blank" moz-do-not-send="true">https://opencv.org/</a><br>
[2] -
<a href="https://urldefense.com/v3/__https://github.com/opencv/opencv/blob/4.x/modules/core/include/opencv2/core.hpp__;!!ACWV5N9M2RV99hQ!JnMeRRKWI0A8qpGkiXzcR0f06AAFEP-dXJV8lT-ZAMcxwE3BhDeGj91EgKkeMudSckPxr_-N9AlNWSGCszOjc6Y$" class="moz-txt-link-freetext" rel="noreferrer nofollow
noopener" target="_blank" moz-do-not-send="true">https://github.com/opencv/opencv/blob/4.x/modules/core/include/opencv2/core.hpp</a><br>
</p>
<blockquote type="cite">
<div style="font-family: Arial, sans-serif; font-size: 14px;
color: rgb(0, 0, 0);"><br>
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<div style="font-family: Arial, sans-serif; font-size: 14px;
color: rgb(0, 0, 0);">Ideas?<br>
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<span></span>
<div style="font-family: Arial, sans-serif; font-size:
14px;"><br>
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<div class="protonmail_quote"> ------- Original Message
-------<br>
On Monday, May 22nd, 2023 at 9:14 AM, Maurizio Cimadamore
<a href="mailto:maurizio.cimadamore@oracle.com" class="moz-txt-link-rfc2396E" rel="noreferrer nofollow
noopener" target="_blank" moz-do-not-send="true"><maurizio.cimadamore@oracle.com></a>
wrote:<br>
<br>
<blockquote type="cite" class="protonmail_quote">
<p><br>
</p>
<div class="moz-cite-prefix">On 22/05/2023 04:12, Rel
wrote:<br>
</div>
<blockquote type="cite">
<blockquote type="cite" style="color: #8c8c8c;">
<pre class="moz-quote-pre">But I believe some more robust
analysis should be made to understand exactly how many APIs can be
supported in this "simple" fashion.
</pre>
</blockquote>
<pre class="moz-quote-pre">Yes, I started to gather such analysis here <a target="_blank" rel="noreferrer nofollow noopener" class="moz-txt-link-freetext" href="https://urldefense.com/v3/__https://github.com/enatai/panamaexperiments__;!!ACWV5N9M2RV99hQ!KOxdK2qmmSzlaaO3kSlSUG2-ifWAVRD6OHlz9NHYvuggmy7NnnNxWvHYcxDm0Vn4gPXlbasjfC-ehIx_KlWNYiU$" moz-do-not-send="true">https://urldefense.com/v3/__https://github.com/enatai/panamaexperiments__;!!ACWV5N9M2RV99hQ!KOxdK2qmmSzlaaO3kSlSUG2-ifWAVRD6OHlz9NHYvuggmy7NnnNxWvHYcxDm0Vn4gPXlbasjfC-ehIx_KlWNYiU$</a>
Currently there is only one happy case [<a target="_blank" rel="noreferrer nofollow noopener" class="moz-txt-link-freetext" href="https://urldefense.com/v3/__https://github.com/enatai/panamaexperiments/blob/main/libcppexperiments/src/main/public/happy.hpp__;!!ACWV5N9M2RV99hQ!KOxdK2qmmSzlaaO3kSlSUG2-ifWAVRD6OHlz9NHYvuggmy7NnnNxWvHYcxDm0Vn4gPXlbasjfC-ehIx_K7Nl50c$" moz-do-not-send="true">https://urldefense.com/v3/__https://github.com/enatai/panamaexperiments/blob/main/libcppexperiments/src/main/public/happy.hpp__;!!ACWV5N9M2RV99hQ!KOxdK2qmmSzlaaO3kSlSUG2-ifWAVRD6OHlz9NHYvuggmy7NnnNxWvHYcxDm0Vn4gPXlbasjfC-ehIx_K7Nl50c$</a> ] which is Point2d class from your foo.hpp file.</pre>
</blockquote>
<p>This is not too surprising - after all the hacky
changes I shared were built around that example.</p>
<p>What I meant for "robust analysis" was to try and
establish how many _real-world_ C++ library can really
be tackled in such a direct approach. My feeling is
"not many" - but I don't have any hard data to back up
this claim.</p>
<p>Maurizio<br>
</p>
</blockquote>
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