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From: rfg@NCD.COM (Ron Guilmette)
Newsgroups: comp.lang.c++
Subject: Re: Smart pointers and stupid people (was: garbage collection...)
Message-ID: <3703@lupine.NCD.COM>
Date: 4 Feb 91 21:42:25 GMT
References: <CIMSHOP!DAVIDM.91Jan7105709@uunet.UU.NET> <3344@lupine.NCD.COM> <4174@osc.COM>
Distribution: comp
Organization: Network Computing Devices, Inc., Mt. View, CA
Lines: 50

In article <4174@osc.COM> tma@osc.UUCP (Tim Atkins) writes:
<
<Obviously, a dereference of a smart pointer MUST happen somewhere in the
<generated code for any real work to get done.

Right.

<Obviously, generated results can be and often are stored away by compiler
<generated code even without counting optimization for later use in any
<context where it can be determined by the compiler that any depended on
<values are constant in particular.

Right.

<Now, if I call something that causes the object to move, then these
<stored away pointers are now invalid.

Right.

<However, HOW DOES THE COMPILER
<know?  I don't know of any way to make it know this strictly from the
<language end...

The compiler need not know.  It is up to the programmer to write code
in which the following *does not* happen:

	generate a dumb pointer value
	call a function which may move the pointed-at object
	use the dumb pointer value generated earlier

My proposal attempted to give the programmer some extra help when it
comes time to make sure sequences of actions like this don't ever happen.

Briefly, my proposal would have allowed to programmer to *restrict* the
area of the program in which dumb pointer values could even be generated.
Once that is done, and the number of places where a dumb pointer value
can even exist is reduced to a minimum, then the programmer would need
to make sure that in all of those (hopefully few) places where the dumb
pointers could exist, no sequences like the one above occur.

In short, if my proposal were adopted, you could still do stupid things,
however you could (with the help fo the compiler) impose restrictions on
the number of places in your program where you could *either* use or
*misuse* dumb pointers.  That's at least a step in the right direction.

-- 

// Ron Guilmette  -  C++ Entomologist
// Internet: rfg@ncd.com      uucp: ...uunet!lupine!rfg
// Motto:  If it sticks, force it.  If it breaks, it needed replacing anyway.