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<p>Hi,<br>
it seems like the binding generator is emitting bindings for
private string fields?</p>
<p><a class="moz-txt-link-freetext" href="https://github.com/gcc-mirror/gcc/blob/master/libstdc%2B%2B-v3/include/bits/basic_string.h#L211">https://github.com/gcc-mirror/gcc/blob/master/libstdc%2B%2B-v3/include/bits/basic_string.h#L211</a></p>
<p>While PhantomData seems some magic Rust thingie:</p>
<p><a class="moz-txt-link-freetext" href="https://doc.rust-lang.org/stable/std/marker/struct.PhantomData.html">https://doc.rust-lang.org/stable/std/marker/struct.PhantomData.html</a></p>
<p>Which is probably used to deal with lifetime of the string char
array (but this is a guess).</p>
<p>Maurizio<br>
</p>
<div class="moz-cite-prefix">On 17/08/2023 05:14, Rel wrote:<br>
</div>
<blockquote type="cite" cite="mid:Ti-jM61LowYfcCfccb85mxSJYO1KLQ9l5MiHNkMXmpv0ZE4bBPvZ87IC6X4BSFgC6EaWQq3ac9pDIMioQY6B-PBsMBBH8n9RlppndLV7WYA=@proton.me">
<span>Hi,</span>
<div><br>
</div>
<div><span>I start to look on rust-bindgen and did few experiments
here:</span></div>
<div><br>
</div>
<div><span><a target="_blank" rel="noreferrer nofollow noopener" href="https://urldefense.com/v3/__https://github.com/enatai/panamaexperiments/blob/main/rust-bindgen/README.md__;!!ACWV5N9M2RV99hQ!JKkwWpDI9MsiWp4MJSA43oz6BbNqfK_Vikm4I5JiB87pf4lcNF8rWmmkvMYVHG1RYRG4-KJx-_sorV5wvpEAntI$" moz-do-not-send="true">https://github.com/enatai/panamaexperiments/blob/main/rust-bindgen/README.md</a></span></div>
<div><br>
</div>
<div><span>My question is around what rust-bindgen generated for
std::string</span></div>
<div><br>
</div>
<div><span>Mostly those are ordinary data fields for which
jextract possibly can generate layout but I don't really
understand purpose of:</span></div>
<div><br>
</div>
<div><span>pub _phantom_0:
::std::marker::PhantomData<::std::cell::UnsafeCell<_CharT>>,</span></div>
<div><br>
</div>
<div><span>and what alternative for that can be from jextract. Is
it some special Rust feature, or?</span></div>
<span></span>
<div class="protonmail_quote"> ------- Original Message -------<br>
On Monday, May 29th, 2023 at 9:00 AM, Maurizio Cimadamore
<a class="moz-txt-link-rfc2396E" href="mailto:maurizio.cimadamore@oracle.com"><maurizio.cimadamore@oracle.com></a> wrote:<br>
<br>
<blockquote class="protonmail_quote" type="cite">
<p><br>
</p>
<div class="moz-cite-prefix">On 29/05/2023 00:20, Rel wrote:<br>
</div>
<blockquote type="cite"> <span>dynamic dispatch</span>
<div><span><br>
</span></div>
<div><span>I tried following example [<a href="https://urldefense.com/v3/__https://github.com/enatai/panamaexperiments/blob/main/libcppexperiments/src/main/public/happy.hpp__;!!ACWV5N9M2RV99hQ!JnMeRRKWI0A8qpGkiXzcR0f06AAFEP-dXJV8lT-ZAMcxwE3BhDeGj91EgKkeMudSckPxr_-N9AlNWSGCtyvUZL0$" rel="noreferrer nofollow noopener" target="_blank" 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>
<div><br>
</div>
<div><span>See test for it [<a 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$" rel="noreferrer nofollow noopener" target="_blank" moz-do-not-send="true">https://github.com/enatai/panamaexperiments/blob/main/cppexperiments/src/test/java/cppexperiments/HappyTests.java#L36</a>]</span></div>
<div><br>
</div>
<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">
<div><br>
</div>
<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">
<div><br>
</div>
<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>
<div><br>
</div>
<span></span>
<div style="font-family: Arial, sans-serif; font-size:
14px;"><br>
</div>
<div class="protonmail_quote"> ------- Original Message
-------<br>
On Tuesday, May 23rd, 2023 at 8:58 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 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>
</div>
<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 target="_blank" rel="noreferrer nofollow
noopener" class="moz-txt-link-freetext" href="https://urldefense.com/v3/__https://opencv.org/__;!!ACWV5N9M2RV99hQ!JnMeRRKWI0A8qpGkiXzcR0f06AAFEP-dXJV8lT-ZAMcxwE3BhDeGj91EgKkeMudSckPxr_-N9AlNWSGC3X8vPfk$" moz-do-not-send="true">https://opencv.org/</a><br>
[2] - <a target="_blank" rel="noreferrer nofollow
noopener" class="moz-txt-link-freetext" href="https://urldefense.com/v3/__https://github.com/opencv/opencv/blob/4.x/modules/core/include/opencv2/core.hpp__;!!ACWV5N9M2RV99hQ!JnMeRRKWI0A8qpGkiXzcR0f06AAFEP-dXJV8lT-ZAMcxwE3BhDeGj91EgKkeMudSckPxr_-N9AlNWSGCszOjc6Y$" moz-do-not-send="true">https://github.com/opencv/opencv/blob/4.x/modules/core/include/opencv2/core.hpp</a><br>
</p>
<blockquote type="cite">
<div style="font-family: Arial, sans-serif; font-size:
14px; color: rgb(0, 0, 0);"><br>
</div>
<div style="font-family: Arial, sans-serif; font-size:
14px; color: rgb(0, 0, 0);">Ideas?<br>
</div>
<span></span>
<div style="font-family: Arial, sans-serif; font-size:
14px;"><br>
</div>
<div class="protonmail_quote"> ------- Original
Message -------<br>
On Monday, May 22nd, 2023 at 9:14 AM, Maurizio
Cimadamore <a target="_blank" rel="noreferrer
nofollow noopener" class="moz-txt-link-rfc2396E" href="mailto:maurizio.cimadamore@oracle.com" moz-do-not-send="true"><maurizio.cimadamore@oracle.com></a>
wrote:<br>
<br>
<blockquote class="protonmail_quote" type="cite">
<p><br>
</p>
<div class="moz-cite-prefix">On 22/05/2023 04:12,
Rel wrote:<br>
</div>
<blockquote type="cite">
<blockquote style="color: #8c8c8c;" type="cite">
<pre class="moz-quote-pre">But I believe some more robust
analysis should be made to understand exactly how many APIs can be
supported in this "simple" fashion.
</pre>
</blockquote>
<pre class="moz-quote-pre">Yes, I started to gather such analysis here <a href="https://urldefense.com/v3/__https://github.com/enatai/panamaexperiments__;!!ACWV5N9M2RV99hQ!KOxdK2qmmSzlaaO3kSlSUG2-ifWAVRD6OHlz9NHYvuggmy7NnnNxWvHYcxDm0Vn4gPXlbasjfC-ehIx_KlWNYiU$" class="moz-txt-link-freetext" rel="noreferrer nofollow noopener" target="_blank" moz-do-not-send="true">https://urldefense.com/v3/__https://github.com/enatai/panamaexperiments__;!!ACWV5N9M2RV99hQ!KOxdK2qmmSzlaaO3kSlSUG2-ifWAVRD6OHlz9NHYvuggmy7NnnNxWvHYcxDm0Vn4gPXlbasjfC-ehIx_KlWNYiU$</a>
Currently there is only one happy case [<a href="https://urldefense.com/v3/__https://github.com/enatai/panamaexperiments/blob/main/libcppexperiments/src/main/public/happy.hpp__;!!ACWV5N9M2RV99hQ!KOxdK2qmmSzlaaO3kSlSUG2-ifWAVRD6OHlz9NHYvuggmy7NnnNxWvHYcxDm0Vn4gPXlbasjfC-ehIx_K7Nl50c$" class="moz-txt-link-freetext" rel="noreferrer nofollow noopener" target="_blank" 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>
<br>
</div>
</blockquote>
</blockquote>
<br>
</div>
</blockquote>
</blockquote>
<br>
</div>
</blockquote>
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