Some comments on restricted pointers in C:
The specifications of the restrict type qualifier referenced by
some of the URL's in the recent oon-digest are out-of-date.
In response to the public comments, substantive changes were made
to give the version that actually went into the standard.
For the final version, see:
http://reality.sgi.com/homer_craypark/c9x/restrict-c99.html
It is the nature of assertions that promote optimization that
they are beneficial only to the extent that they are dangerous.
(If the compiler could check the assertion, or if the
optimization it promotes were safe, you wouldn't need the
assertion.) An advantage of restrict qualifiers, compared to
Fortran dummy argument semantics, is that they are optional, and
can be used only where they make a real difference.
There is a natural extension to C++ that allows reference types
and the "this" pointer to be restrict-qualified. As far as I
know, this extension raises no new issues for the semantics.
It remains to be fully explored whether this is enough for
object oriented programs, or whether "higher level" extensions
(e.g., to iterators) are needed.
Bill Homer
(651) 683-5606 Silicon Graphics, Inc.
homer@cray.com 655F Lone Oak Drive, Eagan, MN 55121
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