From: James Masters <james.d.masters@...>
Date: 2010-05-06T13:45:13+09:00
Subject: Re: How can I call String#replace (rb_str_replace()) in C API?

> >> > I'm really just looking for a way to take a Ruby string VALUE and
> >> > replace the contents of that object with a C string in the most
> >> > efficient method possible.  Can someone help me in doing this or at
> >> > least point me in the right direction?
>
> >> One other option is to fiddle directly with the fields of struct
> >> RString, but I don't recommend that unless you're really dedicated.
>
> > I am thinking about doing this but it would be a pain and probably
> > dangerous as you have mentioned.  I can probably put something
> > together with good performance by tweaking the pointer location and
> > string length but I'll need to get more familiar with the Ruby code
> > before I attempt something like this.  One good thing is that I am
> > creating the Ruby string to be used as the replacement myself in the C+
> > + code on my own so I shouldn't need to do type checking.  If anyone
> > has any pointers on where to find some of the underlying Ruby C data
> > structures (e.g. ELTS_SHARED and STR_ASSOC flags) then I could use it.
>
> BEWARE: if you go this route, you MUST interface correctly with ruby's
> garbage collector, or else your program will crash mysteriously in
> unlikely places. Ruby likes to control not only where struct RString
> is allocated, but also the string buffer it points to. The apis for
> using those internal memory management facilities are definitely not
> public, so this gets icky real fast. I've never tried to do this and
> can't offer any advise about how to fool the garbage collector into
> thinking that a string buffer you allocated is actually kosher.
>
> You're better off trying to call rb_str_replace even tho it is static.
> Or maybe porting your app to 1.9. (Which is a nontrivial effort.)
>
> I can't offer any help with those flags either, other than "Use the
> source, Luke.". The GC issues are likely to be the biggest challenge.

Thanks for the advice :).  Yeah, I was actually thinking about
allocating another Ruby string and doing something similar to what
rb_str_replace does to avoid crashing and GC issues.  But it will
still be tricky.  I wish that this was easier...