Re: Lua and backwards compatibility - was Re: [ANN] Lua 5.3.4 (rc2) now available,

[Marc Balmer <marc@...>]

Am 12.01.17 um 15:54 schrieb Dibyendu Majumdar:
> Hi Tomás,
> 
> On 12 January 2017 at 14:12, tomas <tomas@tecgraf.puc-rio.br> wrote:
>> I work with Lua since 2.1 days and my team maintain code developed initialy
>> with CGILua 3, 20 years ago, and were converted/upgraded to every new Lua
>> version until 5.2 (we are planning to upgrade to Lua 5.3, but we have to
>> wait for the libraries: CGILua, LuaFileSystem, LuaSQL, LuaExpat, LuaSOAP,
>> LuaSec, LuaSocket, CGILua LuaZip, lua-iconv, LPEG, HTK, Dado).  So we did
>> many upgrades and converted our code many times.  Maybe our case is too
>> particular to generalize, but that task was always a simple and easy task.
>>
> 
> Would it not be better though if you could upgrade to the next version
> without having to change things?

Why?  Having to do this also mean reviewing you code, which is not bad.

> I think there are other problems than just upgrading your code.
> 
> Firstly, I see that many libraries are still on 5.1 and so many people
> have not bothered to upgrade. Unless you are full time working on
> maintaining your Lua code (which it seems you are) then it may be
> difficult to keep supporting different versions.

We only support the latest version in our stuff.  To be frank, we don't
even test compile for older versions.  Our "#if LUA_VERSION < 503" lines
are an outright lie and a courtesy to those folks that did not yet have
the time to upgrade their Lua.

> Secondly - and I think this is a bigger pain point - you need to build
> multiple versions of your library as one library cannot support
> various Lua versions. This issue is quite a tragedy I think. For
> instance I get requests to support 5.1 in my VSCode Lua 5.3 debugger.
> I cannot do so without creating another extension dedicated to 5.1.
> Whereas ideally my debugger should just be able to run 5.1 code.
> 
> In my post I suggested providing strong backwards compatibility from
> 5.3 upwards, only because I think as far as the 5.2 and 5.1
> compatibility story is concerned, the 'horse has bolted' so to speak.
> In fact, I think there ought to be a concentrated effort to bring back
> / support as much of 5.1 and 5.2 as possible - to enable more people
> to upgrade to 5.3.

Using third party software of course means that you have to be vigilant,
it is your responsability, not the third party software author's.

>> I think the Lua team always made a good judgement when faced with the
>> problem of introducing a new feature and also an incompatibility.  I don't
>> think this should be changed.
>>
> 
> I think that it is possible to evolve the language without breaking
> compatibility. Just look at how much C++ has evolved since 1998, and
> yet all the old code still works. It requires more effort and thought
> - and sometimes things don't look so nice but that is a price worth
> paying.

Have I already mentioned that I like Lua for what it is?  An slowly
evolving language without batteries included, without to much care for
backwards compatability?  I hope it stays so.

- marc