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Clarify subtle issues with 'eq' in byte-compiled code

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* doc/lispref/objects.texi (Equality Predicates): Explain why
byte-compiled code might compare literal objects with identical
contents as 'eq'.  (Bug#31688)
This commit is contained in:
Eli Zaretskii 2018-06-08 18:06:34 +03:00
parent c6ef3c8321
commit ef35d405b1
1 changed files with 15 additions and 0 deletions
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doc/lispref/objects.texi
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@ -2144,6 +2144,21 @@ Symbols}.
@result{} nil
@end group
@end example
@noindent
@cindex identical-contents objects, and byte-compiler
@cindex objects with identical contents, and byte-compiler
The Emacs Lisp byte compiler may collapse identical literal objects,
such as literal strings, into references to the same object, with the
effect that the byte-compiled code will compare such objects as
@code{eq}, while the interpreted version of the same code will not.
Therefore, your code should never rely on objects with the same
literal contents being either @code{eq} or not @code{eq}, it should
instead use functions that compare object contents such as
@code{equal}, described below. Similarly, your code should not modify
literal objects (e.g., put text properties on literal strings), since
doing that might affect other literal objects of the same contents, if
the byte compiler collapses them.
@end defun
@defun equal object1 object2