[Libreoffice] Removal of rtl::O[U]String[Buffer]::operator sal_{char|Unicode} const *()

[Stephan Bergmann]

Hi all,

As has recently been discussed on #libreoffice-dev, its probably a good 
idea to remove the rather unhelpful conversion operators

   rtl::OString::operator sal_Char const * ()
   rtl::OStringBuffer::operator sal_Char const * ()
   rtl::OUString::operator sal_Unicode const * ()
   rtl::OUStringBuffer::operator sal_Unicode const * ()

(The reason why this came up on IRC this time was that the expression 
"aStr = aStr + cSep" with aStr of type rtl::OString and cSep of type 
sal_Char had a rather non-intuitive meaning, implicitly converting aStr 
into a sal_Char const *, adding the integral value of cSep to that 
pointer, and then converting that modified sal_Char const * back into an 
rtl::OString via the rtl::OString(sal_Char const *) constructor.)

The change will be source-code incompatible, but that is probably 
acceptable:

- The change is ABI compatible (involving only inline C++ functions).

- The ~only legitimate use case for those conversion operators was in 
indexing expressions like aStr[n].  To continue those expressions to 
work, appropriate operator [](sal_Int) member functions will be added to 
the four classes.

- All other uses of the conversion operators should use the getStr() 
member functions.  (Also note that there might be cases where 
translation between, say, rtl::OString and char const * via naive 
application of rtl::OString::getStr() is not appropriate as it 
potentially looses information, when the given rtl::OString instance 
contains NUL characters.  Having the calls to getStr explicitly in the 
code helps auditing in this case.)

My plan is as follows:

- I just pushed 
<http://cgit.freedesktop.org/libreoffice/core/commit/?id=6671fa81db0ecea4ada005bb79f55f08fb440ad4> 
"Removed uses of rtl::O[U]String[Buffer]::operator sal_{char|Unicode} 
const *()." and 
<http://cgit.freedesktop.org/libreoffice/binfilter/commit/?id=34c2ec87db4b6962ded661157056c58163e39821> 
"Removed uses of rtl::O[U]String[Buffer]::operator sal_{char|Unicode} 
const *()."  That clears the current master of all dubious (i.e., 
non-[]) uses of the conversion operators for a Linux x86_64 
--enable-binfilter --enable-dbgutil "make check" build.

- A few more builds (e.g., Windows, Mac OS X) should be done with the 
below patch to ensure that as many dubious uses in 
platform-/configuration-switch-specific code as possible have been 
fixed.  If someone wants to give me a hand here, that would be great.

- The attached no-string-conversion.patch will remove the conversion 
operators and introduce the operator [] replacements.  It can be 
committed to master once the above step is done, in the 3.5 time frame. 
  (If anybody has objections to this, esp. as it nominally breaks 
backwards compatibility at the source level, raise your hands.)

-Stephan
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