Commit 6cc35829 authored by Mattias Engdegård's avatar Mattias Engdegård

Correct 'concat' manual entry (bug#42296)

* doc/lispref/strings.texi (Creating Strings): 'concat' does not
necessarily return a newly allocated string.  This has been the case
at least since 1997 (Emacs 20.3).
parent af4f3a87
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......@@ -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},
......
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