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From "Jens Geyer" <>
Subject Re: Major feature suggestion/observation
Date Wed, 07 Oct 2015 19:29:39 GMT
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.


-----Urspr√ľngliche Nachricht----- 
From: David Bennett
Sent: Wednesday, October 7, 2015 12:26 PM
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) { #>
    <#= prop.Name #>
  <asp:DynamicControl DataField="<#= prop.Name #>" runat="server" />
  <# } #>

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...

David M Bennett FACS

Andl - A New Database Language -

-----Original Message-----
From: Philip Polkovnikov []
Sent: Wednesday, 7 October 2015 8:00 PM
Subject: Re: Major feature suggestion/observation


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 <>:
> Regards
> David M Bennett FACS
> Andl - A New Database Language -
> -----Original Message-----
> From: Roger Meier []
> Sent: Wednesday, 7 October 2015 5:34 AM
> To:
> Cc:
> Subject: Re: Major feature suggestion/observation
> Hi David
> Quoting David Bennett <>:
>> 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: 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

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