Re: [boost] Smart_ptr, Pimpl and BCB5 error

From: Beman Dawes (bdawes_at_[hidden])
Date: 2001-06-07 10:48:49

At 06:50 AM 6/7/2001, John Maddock wrote:

 >> >Same things with scoped_ptr_example_test.cpp.
 >> >Is this bcb5 only bug ?
 >>
 >>I was able to reproduce the problem for the Borland compiler but not 
some
 >>of the others.

I've now verified that the Win32 GCC, Intel, Metrowerks, and Microsoft 
compilers all handle this correctly, while Borland does not.

 >It looks to be a Borland bug: for some reason the destructors of all
 >sub-objects get instantiated when you write:
 >
 >T my_instance;
 >
 >Even if T has all constructors/destructor declared but not defined.
 >
 >This basically makes it impossible to implement the pimpl idon using a
 >smart pointer with this compiler (or any others that have the same
 >problem).  Note that commenting out the static assert is *not* an option:
 >the code compiles then, but issues a warning about deleting an incomplete
 >type - as a result it will not behave correctly at run time - or rather 
it
 >*may* not, depending on which version or the smart_ptr's destructor makes
 >it into the exe (there may be different versions in different translation
 >units, some instantiated "prematurely", others not).

You were smart to figure that out.  In my testing I just commented out the 
assert and dumbly assumed everything was OK because the compile errors went 
away.  But I think that your analysis is correct, including the key point:

It isn't just the Boost smart pointer - any use of a templated pointer to 
an incomplete type could fail if a translation unit with delete of an 
incomplete type happens to be the one linked in.

This looks like a really disastrous bug in the Borland compiler.

I wonder if we've overlooked something?  It seems like Borland users would 
be howling by now if this bug is really biting people.

--Beman