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(Intro to Buffer-Local): Updated warning and

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example relating to changing buffer inside let.
This commit is contained in:
Kim F. Storm 2002-05-13 19:04:27 +00:00
parent 4e792dbd39
commit c152cd2a20
1 changed files with 11 additions and 10 deletions
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21
lispref/variables.texi
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@ -1185,10 +1185,10 @@ be changed with @code{setq} in any buffer; the only way to change it is
with @code{setq-default}.
@strong{Warning:} When a variable has buffer-local values in one or
more buffers, you can get Emacs very confused by binding the variable
with @code{let}, changing to a different current buffer in which a
different binding is in effect, and then exiting the @code{let}. This
can scramble the values of the buffer-local and default bindings.
more buffers, binding the variable with @code{let} and changing to a
different current buffer in which a different binding is in
effect, and then exiting the @code{let}, the variable may not be
restored to the value it had before the @code{let}.
To preserve your sanity, avoid using a variable in that way. If you
use @code{save-excursion} around each piece of code that changes to a
@ -1197,22 +1197,23 @@ different current buffer, you will not have this problem
@example
@group
(setq foo 'b)
(setq foo 'g)
(set-buffer "a")
(make-local-variable 'foo)
@end group
(setq foo 'a)
(let ((foo 'temp))
;; foo @result{} 'temp ; @r{let binding in buffer @samp{a}}
(set-buffer "b")
;; foo @result{} 'g ; @r{the global value since foo is not local in @samp{b}}
@var{body}@dots{})
@group
foo @result{} 'a ; @r{The old buffer-local value from buffer @samp{a}}
; @r{is now the default value.}
foo @result{} 'a ; @r{we are still in buffer @samp{b}, but exiting the let}
; @r{restored the local value in buffer @samp{a}}
@end group
@group
(set-buffer "a")
foo @result{} 'temp ; @r{The local @code{let} value that should be gone}
; @r{is now the buffer-local value in buffer @samp{a}.}
(set-buffer "a") ; @r{This can be seen here:}
foo @result{} 'a ; @r{we are back to the local value in buffer @samp{a}}
@end group
@end example