In article <l2ohazp5q4.fsf@safran.kurims.kyoto-u.ac.jp>, Jacques GARRIGUE
<garrigue@safran.kurims.kyoto-u.ac.jp> wrote:
> Remark that being able to acceed a pointer is not anecdotical. For
> instance, being able to compare physically pointers with < or > means
> restrictions on the garbage collector, that should keep these
> inequalities when moving values around. Most GC's don't.
I know of one important instance where comparing pointers with < and > is
important --- 'genetic order' (birth order) comparisons. In addition to
having a stable sorting order for things like merging ordered lists, genetic
orderings can have other uses. Eiichi Goto of the U. of Tokyo studied this
in the early 1970's. There are a number of GC's that preserve birth order
by squeezing out the garbage even when they relocate objects.
Thus, comparisons of this sort do not require (stable) object id's.
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