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The  kill-ring-yank-pointer Variable

 kill-ring-yank-pointer is a variable, just as  kill-ring is a variable. It points to something by being bound to the value of what it points to, like any other Lisp variable.

Thus, if the value of the kill ring is:

("some text" "a different piece of text" "yet more text")

and the  kill-ring-yank-pointer points to the second clause, the value of  kill-ring-yank-pointer is:

("a different piece of text" "yet more text")

As explained in the previous chapter (see section How Lists are Implemented), the computer does not keep two different copies of the text being pointed to by both the  kill-ring and the  kill-ring-yank-pointer . The words "a different piece of text" and "yet more text" are not duplicated. Instead, the two Lisp variables point to the same pieces of text. Here is a diagram:

Both the variable  kill-ring and the variable  kill-ring-yank-pointer are pointers. But the kill ring itself is usually described as if it were actually what it is composed of. The  kill-ring is spoken of as if it were the list rather than that it points to the list. Conversely, the  kill-ring-yank-pointer is spoken of as pointing to a list.

These two ways of talking about the same thing sound confusing at first but make sense on reflection. The kill ring is generally thought of as the complete structure of data that holds the information of what has recently been cut out of the Emacs buffers. The  kill-ring-yank-pointer on the other hand, serves to indicate--that is, to `point to'---that part of the kill ring of which the first element (the CAR) will be inserted.

The  rotate-yank-pointer function changes the element in the kill ring to which the  kill-ring-yank-pointer points; when the pointer is set to point to the next element beyond the end of the kill ring, it automatically sets it to point to the first element of the kill ring. This is how the list is transformed into a ring. The  rotate-yank-pointer function itself is not difficult, but contains many details. It and the much simpler  yank and  yank-pop functions are described in an appendix. See section Handling the Kill Ring.

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