Pascal Cuoq a écrit :

Elnatan Reisner wrote:

Is there something that can complete this analogy:

(=) is to (==) as Pervasives.compare is to ___?

The simple solution is to number at creation the objects that you want to

physically compare, using an additional field.

Since people are still participating in this topic,

I have a remark. It is more a "what not to do" kind of

remark, but after replying last time, I remembered

that the current algorithm used by OCaml's GC

for compaction does not change the order of blocks

in memory (byterun/compact.c). Therefore, with the

current version, if you make sure in some way

that the values that you want to compare

are allocated directly in the major heap

(there are a couple of ways to do that),

you can theoretically compare their addresses

as unsigned longs: their order will not change

during execution.

But you should still do the comparison

with a unique C function written for this purpose.

If you tried to use a "convert address to int" function,

you would have a race condition between the conversion

of each address and garbage collection.

This is all in very poor taste, even more so than

the usual discussions about == on this list.

Do I get some kind of prize for breaking the record?

Pascal

PS: I wrote a "convert address to int" function for

another purpose once. In order to increase my chances

for the prize, I will provide it here. Someone might be

interested in it. Perhaps someone who maintains a small

library for computing the size of an ML value...

external address_of_value: 'a -> int = "address_of_value"

value address_of_value(value v)

{

return (Val_long(((unsigned long)v)/sizeof(long)));

}