Ada.Strings.Unbounded vs Ada.Containers.Indefinite_Holders

[Victor Porton <porton@narod.ru>]

I am writing an interface to a C library. Some C functions accept either a C 
string pointer or NULL.

I need some way to define an Ada object which could hold values equivalent 
to C strings with possible NULL.

I consider two approaches:

1. Ada.Strings.Unbounded (remind that it can be Null_Unbounded_String which 
is equivalent to NULL C string).

2. Ada.Containers.Indefinite_Holders holding a String.

The first way seems more natural, as a more specialized package is used.

The second way may have the advantage that there is Is_Empty function while 
for unbounded strings I would need to compare with Null_Unbounded_String 
using "=" operator. This may be a little slower. Or does it matter with 
modern compilers?

Hm well, do I understand Null_Unbounded_String correctly? Is 
Null_Unbounded_String really "no string"? or is it just empty string ("")? 
RM2012 should be made more clear on this topic!

-- 
Victor Porton - http://portonvictor.org