diff options
Diffstat (limited to 'doc/lispref/strings.texi')
| -rw-r--r-- | doc/lispref/strings.texi | 13 |
1 files changed, 9 insertions, 4 deletions
diff --git a/doc/lispref/strings.texi b/doc/lispref/strings.texi index 4a7bda57c4e..0dc47f30c43 100644 --- a/doc/lispref/strings.texi +++ b/doc/lispref/strings.texi @@ -248,7 +248,7 @@ properties removed. @defun concat &rest sequences @cindex copying strings @cindex concatenating strings -This function returns a new string consisting of the characters in the +This function returns a string consisting of the characters in the arguments passed to it (along with their text properties, if any). The arguments may be strings, lists of numbers, or vectors of numbers; they are not themselves changed. If @code{concat} receives no arguments, it @@ -269,9 +269,14 @@ returns an empty string. @end example @noindent -This function always constructs a new string that is not @code{eq} to -any existing string, except when the result is the empty string (to -save space, Emacs makes only one empty multibyte string). +This function does not always allocate a new string. Callers are +advised not rely on the result being a new string nor on it being +@code{eq} to an existing string. + +In particular, mutating the returned value may inadvertently change +another string, alter a constant string in the program, or even raise +an error. To obtain a string that you can safely mutate, use +@code{copy-sequence} on the result. For information about other concatenation functions, see the description of @code{mapconcat} in @ref{Mapping Functions}, |