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          University of California at Santa Cruz
Baskin Center for Computer Engineering and Information Sciences 

The following technical report is available electronically or as
a paper copy.  Instructions for getting either follow the abstract.

UCSC-CRL-92-27   (available electronically as ucsc-crl-92-27.ps.Z)
SMART POINTERS:  THEY'RE SMART, BUT THEY'RE NOT POINTERS
Daniel R. Edelson
July 1992, 22 pages (paper copy $6.00)
Abstract:  
There are numerous times when a C++ user could benefit from a pointer
variant that has more functionality than is provided by the basic,
language-defined pointer.  For example, type-accurate garbage
collection, reference counting, or transparent references to
distributed or persistent objects, might be implemented with classes
that provide pointer functionality.  The C++ language directly
supports one kind of pointer substitute, the smart pointer, in the
form of overloadable indirection operators: -> and *.

In this paper we evaluate how *seamlessly* smart pointers can replace
raw pointers.  The ideal is for client code not to care whether it is
using raw pointers or smart pointers.  For example, if a typedef selects
whether raw or smart pointers are used throughout the program, changing
the value of the typedef should not introduce syntax errors.

Unfortunately, C++ does not support pointer substitutes well enough to
permit seamless integration.  This paper presents the desired behavior
of smart pointers in terms of the semantics of raw pointers that the
smart pointers try to emulate. Then, we describe several ways of
implementing smart pointers. For each, we show cases in which the
smart-pointers fail to behave like raw pointers.  From among the 
choices, we explain which is the best for emulating the standard 
pointer conversions.

*Accessors* are similar to smart pointers, but have certain advantages.
This paper discusses the differences between accessors and smart
pointers, and shows why our conclusions about type conversion behavior
also apply to accessors. Whether a programmer prefers smart pointers 
or accessors, this paper shows the limitations and recommends an 
implementation.

This technical report is available electronically through either 
of the following methods:
1.  through anonymous ftp from ftp.cse.ucsc.edu, in /pub/tr. Log in 
    as "anonymous", use your email address as your password, specify 
    "binary" before getting the file.  Uncompress before printing.
2.  by mail to automatic mail server rnalib@ftp.cse.ucsc.edu.
    Put this command on the subject line or in the body of the message:
	@@ send ucsc-crl-92-27.ps.Z from tr
    To get the index or abstract list:
	@@ send INDEX from tr
	@@ send ABSTRACTS.1992 from tr
    To get the list of the tr directory:
	@@ list tr
    To get the list of commands and their syntax:
	@@ help commands

Order paper copies from:  Technical Library, Baskin Center for Computer 
Engineering & Information Sciences, UCSC, Santa Cruz  CA  95064.
Purchase orders are not accepted.  Checks or money orders must be
for U.S. dollars, payable through a U.S. bank, and made out to 
"UC Regents".

Questions:  jean@cse.ucsc.edu

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