Re: [Boost-users] Overcoming AST forward declaration (includes online example)

On Fri, Nov 2, 2018 at 5:32 PM Michael Powell wrote:

On Fri, Nov 2, 2018 at 5:16 PM Michael Powell wrote:

...

Hello,

Please find the example posted here:

http://wandbox.org/permlink/NI2Luvrw1HF7lF1E

A couple of obvious typos resolved, I think the main culprit(s) now are the forward declaration concerns:

https://wandbox.org/permlink/tM6vQilplqDOL4v5

The forward declaration errors now the top most errors: https://wandbox.org/permlink/WeRqkmDR93Wqu8BI

...

The couple of concerns I have in question at the moment are:

* How to best handle variants throughout the grammar. Can I use std::variant? Do I need to use boost::variant? Are there additional Spirit features that make this doable?

* Embedded in that question is what to do with "nil" or "empty statements" which occurs throughout the grammar at times. I wondered if "empty statement" could synthesize "nothing", literally, not contribute to a variant alternative, for instance. Other AST examples seemed to inject a "struct nil {}" pattern, so I figured maybe this was the better approach?

* The real kerfuffle for me at the moment is the AST forward declaration. From what I gather in the protocol, this is an absolute must have. It most occur before Group, and is also used by Message.

Thoughts? Suggestions?

And, please, before you suggest there are "proto compilers" already available: yes, I know, I've been down that road. I am not looking to parse the proto itself, per se, but rather do some code generation for target language artifacts other than the proto itself.

Toward which end, I am also investigating a protoc compiler plugin approach. But I figured, I'd pursue this as a viable path to solving the problem as well, notwithstanding the above challenges.

Thanks in advance!

Cheers,

Michael Powell