Re: [boost] [review] Shmem

From: Cliff Green (cliffg_at_[hidden])
Date: 2006-02-16 19:51:52

> It looks to me that you are talking about different 
>things. I think
> Ion agrees about invariants but advocating an interface 
>that can be
> used without exceptions, to make the library accessible 
>to the
> platforms with no exception available. And without 
>exceptions, you
> can't ensure that no object with invalid state is 
>constructed. So
> there is two choices - or to provide an exception-only 
>interface and
> strong invariants, or to allow the library to be used in 
>a restricting
> embedded environment.

Someone please correct me if I'm wrong, but doesn't the 
GCC C++ std library (and maybe others) support a "no 
exception" compile time flag, by replacing thrown 
exceptions with an assert? Within the library, every place 
an exception would be thrown goes through a function that 
has a compile time conditional on either throwing the 
appropriate std lib exception or calling assert.

I think the goal of providing alternate interfaces for 
embedded environments where exceptions are not supported 
is misguided. Note that support for replacing the thrown 
exception with assert is NOT supporting alternate 
interfaces to the library - it is supporting alternate 
error recovery mechanisms, which is a different thing. I 
wonder how environments without exception support handle 
the C++ std library, since exceptions are part of the 
standard (and I haven't looked at the EC++ effort, which I 
think was promoted by Dinkumware and maybe others).

I'm a very big believer in preconditions, invariants, etc. 
I can provide real-world experience (multiple large-scale 
projects) about the problems caused by two-phase 
construction (or more specifically, the easy misuse and 
hidden costly bugs introduced as part of a two-phase 
construction design). If we were still in the early 90's, 
where C++ exceptions were not the norm (or not well 
implemented), it would be a different story (e.g. the ACE 
library is full of two-phase construction designs due to 
it's vintage, but if the ACE people were starting from 
scratch today, it would be a far different story). I guess 
I just don't see where Shmem is fundamentally different 
from other Boost libraries, where it must support 
alternate interfaces for exception-less environments.

I haven't recently looked at Shmem, so I'm not criticizing 
it's (most likely excellent) quality. I'm just chiming in 
with Dave A and others about class design principles, of 
which I hold strong opinions.

Cliff