snap

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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.


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