Re: c++ "with" keyword

[dewar@gnat.com (Robert Dewar)]

> Any language construct that fails in this regard (like with) is very bad 
> - period.

But look carefully at what you are saying. We are talking about a structure
or class whose members are visible to the client of the library. The change
we are talking about is adding a new member to the structure. You cannot
possibly think that such a change can be done in a guaranteed 100%
upwards compatible manner. That's absurd.

(for example, at the very least the size of an instance will change).

Furthermore, the situations under which adding this member will cause
specifically a difficulty with WITH are very marginal. It is indeed
far more likely that the addition of a member will cause other compatibility
differences.

If you disagree, give a specific realistic example of what you are talking
about. I certainly can't think of one!

> Again, our perspectives on what is important is different, as a library 
> maintainer, I see this as much more important an issue than you do.
> 
> 

Again, remember we are talking not about the writer of the library but the
user. Suppose the user obtains an offset of a member of the structure, and
you add a new member. Well then the offset changes, and that could cause
arbitrary chaos of a really difficult nature. Would you use this to argue
that it should be impossible to obtain the offset of a structure member.
Of course not. 

If a user uses WITH on one of your structs, then it is still extremely
unlikely that your change will cause trouble.

I really think that you need to give an example. Talking in generalities
is always misleading. If you think something is dangerous don't just go
around sounding red alert. Instead give a specific technical example :-)