Re: Correct way to push an empty string?

[Tim Hill <drtimhill@...>]

> On Aug 24, 2015, at 12:12 PM, Roberto Ierusalimschy <roberto@inf.puc-rio.br> wrote:
> 
>> what about making backwards compatible change in the future API releases?
>> Given that responsible API user will need to check the pointer for NULL
>> anyway (at least in the case above), maybe it would be reasonable to embed
>> this check in the API and push synthetic empty string in case len is zero
>> and the pointer is NULL. Either it will be done inside the API or each and
>> every developer will be forced to write additional wrappers on top of
>> pushlstring (or write unreliable code)...
>> This change does not seem to break anything. Just adding this point to
>> the documentation will force people to, well, read documentation in
>> some buggy situations like this.
> 
> I thought about that. It is not true that "responsible API user will
> need to check the pointer for NULL anyway".  I checked all uses of
> lua_pushlstring in the standard libraries and some other libraries I
> wrote (without knowing that it was wrong to pass NULL): I did not find
> a single case that needed that check.  (Even though many places could
> call lua_pushlstring with a zero length, none would pass NULL as a
> pointer.) To make everybody pay for a check that seems to be rarely
> needed is not a good idea. (This is a C API, after all.)
> 
> -- Roberto
> 

+1 on this. I just walked our 22,000 lines of interface code in the current project, and of the 45 places where lua_pushlstring() was called, only one would ever pass a NULL (and of course was an easy fix). I think a doc fix is all that is needed.

OTOH, adding a (debug version only) assert() might not be a bad thing.

—Tim