[Fribidi-discuss] How much to hide the internal structure of FriBidiEnv?

[Omer Zak]

I am now in midst of finalizing the FriBidiEnv patch, which adds an
argument to all important FriBidi procedures.  The extra argument allows
different processes and different modules of the same software package to
run FriBidi with different environments (and achieve thread-safety,
customized debug modes, etc.).

An issue was raised, over which I would like to know the opinions of the
list subscribers.

There are two possible ways to declare FriBidiEnv:

1. Expose the whole structure in fribidi_env.h - the client software may
   allocate memory for FriBidiEnv in whatever way it wants - static, on
   the stack, on the heap.  It is possible to avoid having to check for
   memory allocation success.

   On the other hand, if the structure of FriBidiEnv changes, the client
   software has to be recompiled.

   It is easy for an application to request the default FriBidiEnv
   instance, by passing a NULL pointer to FriBidi procedures (in operating
   systems, which support global static variables).

2. Declare FriBidiEnv to be an opaque datatype, and treat it as an handle.
   The length of FriBidiEnv will be the same as that of a void* pointer.

   The contents of the data structure will be hidden from the client
   application.

   An application has to explicitly allocate ("open") and deallocate
   ("close") memory to be referenced by a FriBidiEnv handle.

   It is more difficult for an application to use NULL as the value of
   FriBidiEnv, because it may also be the result of memory allocation
   failure.  Furthermore, it is necessary for a robust application to
   check that FriBidi successfully "opened" FriBidiEnv.


Personally I prefer the simplicity of (1).  What do you think?
                                             --- Omer
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