[Sorry -- I only just subscribed so missed any earlier commonents on the dev
list]
Your experience parallels mine, except that I'm a compiler guy so I've leant
more towards language-based solutions, and I've written a couple of template
engines.
Re simple stuff: agreed. Simple stuff is simple.
Re performance: not interested. There are situations where the speed of code
generation matters, and this is not one of them.
Re features of the template language: absolutely. A language that is not
'Turing Complete' (whatever that means in this context) will run into problems
it cannot solve.
FWIW TC means state, iteration and alternation, which covers your loops and
filters. The only way to get there is to include a full-blown macro processing
language or equivalent (I've written one of those too). Look at Tex, m4 for
examples. Good page here too: https://en.wikipedia.org/wiki/Template_processor.
The key thing is Model View separation: the C++ parse provides the data model
and the template language generates the source code View. With this separation
and a suitable data model, there should (almost) never be a need to change
anything except individual templates.
In practice what I have done is to write special purpose functions in the host
language and call them from the template. Your keyword example would require a
language-specific callable function for each supported language to check and
perhaps mangle identifiers.
But this project is only reasonable if the templating tool exists, and it is
sufficiently powerful that the conversion is largely mechanical, and there are
sufficient regression tests to check the results.
Of all the tools I know, this one
https://theantlrguy.atlassian.net/wiki/display/ST4/StringTemplate+4+Documentation
is the one that is most likely to be suitable.
Regards
David M Bennett FACS
Andl - A New Database Language - andl.org
-----Original Message-----
From: Jens Geyer [mailto:jensge...@hotmail.com]
Sent: Thursday, 8 October 2015 6:30 AM
To: Thrift-Dev <dev@thrift.apache.org>
Cc: u...@thrift.apache.org
Subject: Re: Major feature suggestion/observation
Hi *,
Please, FUP @ dev list. Thank you.
I agree that the existing code generation code has some potential, in many
ways. I even agree that it could be a good idea to rethink some of the
concepts. But the question I raised a few hours earlier (on the dev list) was
precisely targeted at what I think is the key here: How many will it cost and
how much will we really benefit from converting everything into a
template-based generator?
Having a good portion of (production code) experience in both template based
and non-template based codegen worlds, I believe I can speak with enough
authority regarding this whole matter. From my experiences, both ways have
their pros and cons. For simple, example-like stuff, everything is easy, with
or without templates. But in the real world, you will face lots of special
cases making your life harder. The good thing about a code-based generator is,
that there are typically more options to deal with such things in a performant
and convenient way. Trying to express these in a template language can become a
pain very quickly. Templates are as good as the template language and system
reaches. It typically starts to get complex with things that need to be
enumerated and filtered. Bringing loops and conditions into a template-based
engine is a challenging task, this is where the good, the bad and the ugly
start to become separated.
In fact, given a fairly complex project, there is not much difference in what
you do when there is need to add features that are not supported by your coded
generator or template language: You change the implementation.
Just one example, that is still sort of an general issue across all
languages: reserved keywords. Besides the few obvious Thrift IDL related
keywords, each language has its own special set of reserved keywords.
Putting all of them into one single global list that is used by all (!) languages
is something that I don't like very much, yet we still have it in the Thrift
compiler. Furthermore, each language has its own way how to deal with reserved
keywords: Some allow for a prefix like @ or &. We also have some additional,
per-language treatment in the Thrift compiler as well to deal with these
subtleties. Although more to the point in my opinion, these solutions are by no
means perfect either.
Now think about, how a template-based could generator help with that specific
issue? I don't mean the question whether or not it is possible /somehow/ - it
should indeed be sort of a neat and clean solution, a significant improvement
over what we already have.
You may get the impression that I'm against templates, but that's not true, I
am not. Templates are a very powerful tool. But I strongly doubt that switching
Thrift from one to the other just because it is possible will produce enough
net gain to justify the efforts needed. In my humble opinion we should spent
that time and developer-power more wisely.
$0,02,
JensG
-----Ursprüngliche Nachricht-----
From: David Bennett
Sent: Wednesday, October 7, 2015 12:26 PM
To: u...@thrift.apache.org
Subject: RE: Major feature suggestion/observation
[I'm wary of Boost. It's quite a commitment. But if needs must...]
I had a quick look: it seems that the generation is achieved while compiling
the code using C++ templates. This is not what I had in mind at all. It should
be possible to edit a template without a C++ recompile.
Here is a simple program in T4. You can probably see how it works with no
further explanation.
<table class="detailstable">
<# foreach (var prop in data.Properties) { #>
<tr>
<th>
<#= prop.Name #>
</th>
<td>
<asp:DynamicControl DataField="<#= prop.Name #>" runat="server" />
</td>
</tr>
<# } #>
</table>
But this is only suitable for C#, and rewriting the compiler is definitely a
step too far. There is Cheetah for Python and lots of other HTML template
engines, but in a quick review I could find nothing suitable. Maybe I just
imagined there was a solution...
Regards
David M Bennett FACS
Andl - A New Database Language - andl.org
-----Original Message-----
From: Philip Polkovnikov [mailto:polkovnikov...@gmail.com]
Sent: Wednesday, 7 October 2015 8:00 PM
To: u...@thrift.apache.org
Subject: Re: Major feature suggestion/observation
David,
Default codegen solution in C++ world is Boost Karma. Though I'm unsure if it
is OK to make users that would like to compile thrift compiler set boost up and
wait several minutes until thrift compiles.
2015-10-07 3:11 GMT+03:00 David Bennett <da...@yorkage.com>:
Regards
David M Bennett FACS
Andl - A New Database Language - andl.org
-----Original Message-----
From: Roger Meier [mailto:ro...@bufferoverflow.ch]
Sent: Wednesday, 7 October 2015 5:34 AM
To: u...@thrift.apache.org
Cc: dev@thrift.apache.org
Subject: Re: Major feature suggestion/observation
Hi David
Quoting David Bennett <da...@yorkage.com>:
I'm a compiler guy (amongst other scars). I was somewhat surprised
when I opened up the Thrift compiler to discover that it uses
industrial strength parsing (for a very slim language) and a
hand-rolled, ad hoc source code generator (for a serious backend
problem). I had expected the exact opposite.
After reading a few comments on this list I think a number of the
shortcomings of Thrift result from this. The compiler may be
'tweakable' but it sure ain't configurable. The precise content of
the generated code (and how to alter it) is an ever present problem.
My suggestion is that the backend of the compiler should be entirely
rewritten using modern code generation technology and a selection of
'skeletons' provided as separate text files. Anyone who wanted to
tweak the output for any of their special use cases could easily copy
and modify an individual skeleton without having to venture into the
dark recesses of the C++ compiler.
Did you had a look at the JIRA issues related to rewrite and changes
on the compiler?
I found this one: https://issues.apache.org/jira/browse/THRIFT-1173.
It's right on the money, but seems to have been silently abandoned 4 years ago.
Looks like the guy who tackled it didn't know enough about template
tools to make it happen, despite the best of intentions.
I didn't find anything else remotely similar, but lots of requests for
little tweaks that would become no-brainers with a template system.
Have you seen the python variant? This was another try to do it again.
No. Which issue?
I have seldom seen some successful rewrites, usually it takes too
long to bring them to the same level. Personally, I'm a fan of evolution.
Agree absolutely. The only way to tackle this kind of transformation
is to treat the existing compiler as the spec and set out to replicate
it, to the point of being able to pass identical regression tests.
That works, but it takes a while just to get back where you started.
With luck, the initial batch of skeletons could be extracted directly
from the existing compiler. It's still a biggish job.
[Side digression: for some languages code generation is not really
needed. The language has sufficient abstraction capability to
implement the IDL directly. Since there are other languages that do
not, we are stuck with code generation.]
The biggest choice is: which product to use for the code generation?
I have a little familiarity with T4 and the ANTLR StringTemplate, and
I've hand-rolled a couple of my own but there are heaps of others out
there. Maybe it all comes down to what you're used to.
I'm not sure I'm quite ready for the investment of time.
Feel free to rewrite the compiler and provide a test suite for review.
Probably not -- Andl is keeping me busy enough for now. I was kind of
hoping someone with C++/compiler experience could at least nominate a
suitable template product. I don't know one, and a quick look at
cpptemplate does not leave me filled with joy. Without this, it's just
far too much work.
Improving the test suites across languages, improving CMake, fixing
bugs and many other topics to improve on Thrift has much higher
priority than rewriting something we already have.
I get that. What Thrift does and what it needs don't really overlap my
skill set (or my interests) all that well, but I will keep an eye out
for somewhere I can help.
best!
Roger
PS: dev list is a better place for such discussions.
Thanks. I'll look into that.
Regards
David M Bennett FACS
