Info Catalog elisp: Low-Level Kill Ring elisp: The Kill Ring

elisp: Internals of Kill Ring

 
 31.8.6 Internals of the Kill Ring
 ---------------------------------
 
 The variable ‘kill-ring’ holds the kill ring contents, in the form of a
 list of strings.  The most recent kill is always at the front of the
 list.
 
    The ‘kill-ring-yank-pointer’ variable points to a link in the kill
 ring list, whose CAR is the text to yank next.  We say it identifies the
 front of the ring.  Moving ‘kill-ring-yank-pointer’ to a different link
 is called “rotating the kill ring”.  We call the kill ring a “ring”
 because the functions that move the yank pointer wrap around from the
 end of the list to the beginning, or vice-versa.  Rotation of the kill
 ring is virtual; it does not change the value of ‘kill-ring’.
 
    Both ‘kill-ring’ and ‘kill-ring-yank-pointer’ are Lisp variables
 whose values are normally lists.  The word “pointer” in the name of the
 ‘kill-ring-yank-pointer’ indicates that the variable’s purpose is to
 identify one element of the list for use by the next yank command.
 
    The value of ‘kill-ring-yank-pointer’ is always ‘eq’ to one of the
 links in the kill ring list.  The element it identifies is the CAR of
 that link.  Kill commands, which change the kill ring, also set this
 variable to the value of ‘kill-ring’.  The effect is to rotate the ring
 so that the newly killed text is at the front.
 
    Here is a diagram that shows the variable ‘kill-ring-yank-pointer’
 pointing to the second entry in the kill ring ‘("some text" "a different
 piece of text" "yet older text")’.
 
      kill-ring                  ---- kill-ring-yank-pointer
        |                       |
        |                       v
        |     --- ---          --- ---      --- ---
         --> |   |   |------> |   |   |--> |   |   |--> nil
              --- ---          --- ---      --- ---
               |                |            |
               |                |            |
               |                |             -->"yet older text"
               |                |
               |                 --> "a different piece of text"
               |
                --> "some text"
 
 This state of affairs might occur after ‘C-y’ (‘yank’) immediately
 followed by ‘M-y’ (‘yank-pop’).
 
  -- Variable: kill-ring
      This variable holds the list of killed text sequences, most
      recently killed first.
 
  -- Variable: kill-ring-yank-pointer
      This variable’s value indicates which element of the kill ring is
      at the front of the ring for yanking.  More precisely, the value is
      a tail of the value of ‘kill-ring’, and its CAR is the kill string
      that ‘C-y’ should yank.
 
  -- User Option: kill-ring-max
      The value of this variable is the maximum length to which the kill
      ring can grow, before elements are thrown away at the end.  The
      default value for ‘kill-ring-max’ is 60.
 

Info Catalog elisp: Low-Level Kill Ring elisp: The Kill Ring