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elisp: Unloading

 
 15.9 Unloading
 ==============
 
 You can discard the functions and variables loaded by a library to
 reclaim memory for other Lisp objects.  To do this, use the function
 ‘unload-feature’:
 
  -- Command: unload-feature feature &optional force
      This command unloads the library that provided feature FEATURE.  It
      undefines all functions, macros, and variables defined in that
      library with ‘defun’, ‘defalias’, ‘defsubst’, ‘defmacro’,
      ‘defconst’, ‘defvar’, and ‘defcustom’.  It then restores any
      autoloads formerly associated with those symbols.  (Loading saves
      these in the ‘autoload’ property of the symbol.)
 
      Before restoring the previous definitions, ‘unload-feature’ runs
      ‘remove-hook’ to remove functions in the library from certain
      hooks.  These hooks include variables whose names end in ‘-hook’
      (or the deprecated suffix ‘-hooks’), plus those listed in
      ‘unload-feature-special-hooks’, as well as ‘auto-mode-alist’.  This
      is to prevent Emacs from ceasing to function because important
      hooks refer to functions that are no longer defined.
 
      Standard unloading activities also undoes ELP profiling of
      functions in that library, unprovides any features provided by the
      library, and cancels timers held in variables defined by the
      library.
 
      If these measures are not sufficient to prevent malfunction, a
      library can define an explicit unloader named
      ‘FEATURE-unload-function’.  If that symbol is defined as a
      function, ‘unload-feature’ calls it with no arguments before doing
      anything else.  It can do whatever is appropriate to unload the
      library.  If it returns ‘nil’, ‘unload-feature’ proceeds to take
      the normal unload actions.  Otherwise it considers the job to be
      done.
 
      Ordinarily, ‘unload-feature’ refuses to unload a library on which
      other loaded libraries depend.  (A library A depends on library B
      if A contains a ‘require’ for B.)  If the optional argument FORCE
      is non-‘nil’, dependencies are ignored and you can unload any
      library.
 
    The ‘unload-feature’ function is written in Lisp; its actions are
 based on the variable ‘load-history’.
 
  -- Variable: unload-feature-special-hooks
      This variable holds a list of hooks to be scanned before unloading
      a library, to remove functions defined in the library.
 

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