bug#40671: [DOC] modify literal objects

[Paul Eggert]

On 4/26/20 12:22 PM, Philipp Stephani wrote:

> nobody "accidentally" writes code like this.

Not code like my trivial example, no. But the underlying problem is all too
common. After all, it's why Emacs is dumping core here - the Emacs Lisp
interpreter is using C code like that to implement some Lisp strings.

> We could either (a) remove the notion of
> "constant" objects so that all objects become mutable, (b) introduce
> static type checking including const-correctness so that attempting to
> mutate a "constant" object would fail byte-compilation, and/or (c)
> make it an error to mutate such objects at runtime (similar to (set t
> nil)).

Neither (a) nor (b) sound very practical. Emacs formerly did a better job at (c)
and could do so again, so it's an obvious way to move forward here.