hana VS sml

I like boost::hana. Wish I had more chances to use it at work.

And then there's also the longstanding issue with default member initializers -- https://github.com/boostorg/hana/issues/409 -- which was a deal-breaker.The PROP system avoids this issue precisely by having the macro be as local as possible: the default member initializer is outside the macro. It does this while still letting you attach additional PropAttribs metadata (I'm not sure what additional metadata attachment looks like in Hana? haven't really tried). Default values and additional attributes are by and large quite more important to me in my use cases for reflection (component types in game ECS) than range syntax (everything I've needed and can think of needing is covered by for-each loop).

oh yes definitely, but I meant more the particular way I've done it so far - which has been to implement something similar to boost::hana::is_valid(), to make it take the least amount of boilerplate code per-use-case as possible: zero additional lines of code.

Boost.Hana developers measured a very noticeable 15% decrease in compile time switching from a function call (admittedly -- with an additional layer of wrapper) to a raw static_cast. foonathan himself saw a little over a 5% decrease in his actual code. miki151 saw about a 3% improvement from replacing move with MOV only, ignoring forward. In a completely synthetic benchmark where I just generate a ton of move calls in a row, I get a little over 40% decrease in compile time.

Anyway the need is not complicated, I need both entry and exit functions from every state, optionally allowing these functions to be coroutines (that's special sauce but for later), and an explicit state transition table which also have a way to say that a state can be accessed at any point. Also allow states to be state machines, optional FSM hierarchies. If you ignore the coroutine stuff it's pretty standard features these days, except that - Boost.MSM is quite archaic now (it was so novel when it was first released...) although it allows most of the features I talked about, I just think it will complicate my code unneecessarilly; - Boost-Ext.SML (not Boost) is almost perfect except it doesnt have entry/exit functions on states for some reason. Also last time we (as in in livestream) tried it in prototypes it didnt compile on msvc XD - Boost-Ext.SML2 is even better but still doesnt have entry/exit functions although it's in the plans.

Hello all. Being a huge fan of state machine and coroutines, I have been browsing around for examples of what other people do combine these two. I have been using boost-ext/sml for quite many projects and are quite happy about that. But when transitioning to code that relies on coroutines, I would like to write entry/exit/actions/guard methods that uses coroutines and where I can co_await on awaitables from Asio and more recently "Boost Async".

boost-ext/sml: quite modern way of doing state machines using a DSL

I recently was troubleshooting a crash that backtraced through the boost::sml library [0]. The crash didn't actually have anything to do with the library, but it was used as the core event loop.

The backtrace -- as in, just the output from running `bt` in GDB -- was over a thousand wrapped lines long. There were ~5 stack frames that took up 200 lines of console each to print just the function name. That product's debug builds recently hit the 2GB line, which is enough that old versions of binutils complain.

I don't know what the solution is. There's some really neat stuff you can do with template metaprogramming, and in stripped release builds it compiles down extremely tiny. Plus the code is very clean to read. But it does feel like there isn't any kind of central vision for the C++ debugging experience, and bad interactions between highly-complex modern C++ typing, the compiler, and the debugger are probably only going to get worse unless somebody (the ISO committee? Vendors?) thinks really hard about debugging support.

[0]: https://github.com/boost-ext/sml

I'm a big fan of MSM but what you're experiencing is pretty normal for template-heavy libraries built on C++03 machinery (emulation of variadic templates is the usual culprit). It's probably not the answer you're hoping for, but the real solution is to switch to a library with more modern foundations. (I've been happily using [Boost::ext].SML for a few years but I'm reluctant to strongly recommend anything in particular since I haven't re-explored the problem space since I found it.)

The Boost one that you mention, seems to be one that it's kinda old. A "successor" of sorts is Boost SML. I've not used it yet, but certainly the first impressions are very good.

Or Boost.Sml

At our company, we rely a lot on https://github.com/boost-ext/sml

I'm a big fan of boost::sml for representing state machines.

https://github.com/boost-ext/sml (State Machine DSL and backend for perfomance)