🚀 go-pugleaf

In article <4k60bd$aa1@solutions.solon.com>,
Jerry Coffin <jcoffin@rmii.com> wrote:
 >In article <4jv6o8$coj@solutions.solon.com>, 
 >schwarz@mips.complang.tuwien.ac.at says...
 >> 
 >> My understanding is that a conversion to a (void *) followed by a conversion
 >> to the original pointer type is the identity mapping; in other words, the
 >> mapping a C compilers uses between (void *) and any other pointer type is
 >> bijective.
 >
 >Hmm...I'm not sure what "bijective" means (my dictionary doesn't include it) 
 >the basic idea here seems to be correct: "A pointer to any incomplete or 
 >object type may be converted to a pointer to void and back again; the result 
 >shall compare equal to the original pointer."  ($6.2.2.3)

Actually, he's mistaken about the "bijective" bit, the map is only
"injective". Bijective means the mapping is two-way on both domains,
ie a cast from a (Type *) to a (void *) can be cast back (true) _and_
that a cast from a (void *) to a (Type *) can be cast back (generally
false). (Since the mapping from (Type *) to (void *) is injective, it
follows that the mapping from (void *) to (Type *) is surjective.)

regards, ct