Re: [ gnuplot-Patches-992149 ] String variables revisited

[Volker D. <v.d...@we...>]

Ethan Merritt wrote:
> Consider a typical call site, one of the 98 you counted:
> 
> set.c (set_fontpath) line 1801:
> 
> if (isstring(c_token)) {
> int len;
> char *ss = gp_alloc(token_len(c_token), "tmp storage");
> len = (collect? strlen(collect) : 0);
> quote_str(ss,c_token,token_len(c_token));
> collect = gp_realloc(collect, len+1+strlen(ss)+1, "tmp fontpath");
> 
> I am not clever enough to re-write isstring() and quote_str() such
> that the code at this call site works when the length of the string
> changes mid-stream. So trying to be clever in isstring() and
> quote_str() paradoxically makes *more* work, since every call site
> would have to be inspected and re-written for compatibility.
> 
Yes, but this I think this is easy:  I took a look at my old `value
substitution` patch (the python like syntax of "%(foo).2f"):
There are two functions: quote_str and m_quote_capture.
Using quote_str you will have to do memory allocation yourself,
whereas m_quote_capture will do allocation for you if I remember
correctly.  My old patch replaced (hopfully) all the invocations
of quote_str with m_quote_capture and did substitution there. 

> If the program were being re-written from scratch, then yes.
> But in the interest of sanity and not introducing 98 possible
> new bug sites, I would rather go for a solution that leaves the
> input code intact ...
>
I think 98 sites which do memory allocation themself is more
dangerous than replacing 98 call sites with one tested and
correct call to m_quote_capture.

Regarding the discussion about late evaluation:  I would like
to _object_ to late evaluation.  Late evaluation will intruduce
much more problems in user space than it will solve.  If I
construct a string (regardless if done by the '' + trick or sprintf
or anyting else) I expect it to be the way I constructed it;
at least that's the behavior of all programming languages I am
familiar with.  I do not see any problem which could be solved
easier with late evaluation, at least not from user side:  It is
very easy to reconstruct the string if a variable change should
be reflected in the string.

IMHO the substitution should be done right during parsing,
no late evaluation and m_quote_capture is a good place for
it.

Volker
 
--
Volker Dobler
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