Re: don't understand setq-default

[Thibaut Verron]

On 2021-04-19 5:06 a.m., Emanuel Berg via Users list for the GNU Emacs 
text editor wrote:
> So the pecking order is:
>     local var
>     global var
>     local default
>     global default
I'm not sure if that's a good way to look at it.

A global variable has a (global) value. You can give it a buffer-local 
value in a specific buffer (with make-local-variable or setq-local), in 
which case what you get is another variable with the same name, which is 
buffer local. The buffer does not see the global variable anymore. It 
doesn't have a default value, but its initial value is that of the 
global variable.

On the other hand, a variable which is buffer-local-when-set is 
essentially always buffer-local. In that case, it has a default value 
(which is global) and possibly a buffer-local value. For those 
variables, setq is the same as setq-local: it creates a buffer-local 
variable if one does not exist, and sets the buffer-local value.

If you really want to think of it in terms of precedence, it would be 
local value > default value > global value. But I can't really imagine a 
situation where a local variable would have the same name as a global 
variable and a default value different from the global value.

So I find it more natural to think of it as two different situations:

- for a global variable which you made local in some buffer, the 
precedence is local value > global value;

- for a buffer-local-when-set variable, the precedence is (local) value 
> (global) default value.