snap
v. To replace a pointer to a pointer with a direct pointer;
to replace an old address with the forwarding address found there.
If you telephone the main number for an institution and ask for a
particular person by name, the operator may tell you that person's
extension before connecting you, in the hopes that you will `snap
your pointer' and dial direct next time. The underlying metaphor
may be that of a rubber band stretched through a number of
intermediate points; if you remove all the thumbtacks in the
middle, it snaps into a straight line from first to last. See
chase pointers.
Often, the behavior of a trampoline is to perform an error
check once and then snap the pointer that invoked it so as
henceforth to bypass the trampoline (and its one-shot error check).
In this context one also speaks of `snapping links'. For
example, in a LISP implementation, a function interface trampoline
might check to make sure that the caller is passing the correct
number of arguments; if it is, and if the caller and the callee are
both compiled, then snapping the link allows that particular path
to use a direct procedure-call instruction with no further
overhead.
