What's the purpose of things like `default-truncate-lines'?

What's the purpose of things like `default-truncate-lines'?

[David Kastrup]

I read

    default-truncate-lines is a variable defined in `src/buffer.c'.
    Its value is nil

    Documentation:
    Default value of `truncate-lines' for buffers that do not override it.
    This is the same as (default-value 'truncate-lines).

    [back]

If it is the same as (default-value 'truncate-lines), why do we have a
separately named variable?

Is this just a technical necessity for some reason?

I am asking because `default-truncate-lines' is documented as a
variable of its own in the Elisp manual, and I am not sure whether
that makes any sense.  Maybe it would be better to point out that
`truncate-lines' is automatically buffer-local and thus its default
should be set with `setq-default'.

-- 
David Kastrup, Kriemhildstr. 15, 44793 Bochum

Re: What's the purpose of things like `default-truncate-lines'?

[Richard Stallman]

    If it is the same as (default-value 'truncate-lines), why do we have a
    separately named variable?

History.

Re: What's the purpose of things like `default-truncate-lines'?

[David Kastrup]

Richard Stallman <rms@gnu.org> writes:

>     If it is the same as (default-value 'truncate-lines), why do we have a
>     separately named variable?
>
> History.

Is it then appropriate to remove the reference to
default-truncate-lines from the Elisp manual, as
default-truncate-lines does not appear to have usefulness of its own?

-- 
David Kastrup, Kriemhildstr. 15, 44793 Bochum

Re: What's the purpose of things like `default-truncate-lines'?

[Stuart D. Herring]

>>     If it is the same as (default-value 'truncate-lines), why do we have
>> a
>>     separately named variable?
>>
>> History.
>
> Is it then appropriate to remove the reference to
> default-truncate-lines from the Elisp manual, as
> default-truncate-lines does not appear to have usefulness of its own?

More than that; unless I'm mistaken, it doesn't actually attach to the
default value of `truncate-lines'.  Does it actually do anything
interesting at all?

Davis

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Re: What's the purpose of things like `default-truncate-lines'?

[Richard Stallman]

    More than that; unless I'm mistaken, it doesn't actually attach to the
    default value of `truncate-lines'.

Yes it does.

Re: What's the purpose of things like `default-truncate-lines'?

[Richard Stallman]

    Is it then appropriate to remove the reference to
    default-truncate-lines from the Elisp manual, as
    default-truncate-lines does not appear to have usefulness of its own?

I don't see a reason to remove its docs.  Some code might use it.

Re: What's the purpose of things like `default-truncate-lines'?

[David Kastrup]

Richard Stallman <rms@gnu.org> writes:

>     Is it then appropriate to remove the reference to
>     default-truncate-lines from the Elisp manual, as
>     default-truncate-lines does not appear to have usefulness of its own?
>
> I don't see a reason to remove its docs.  Some code might use it.

But for understanding existing code, the DOC string should be enough.
Things that are documented in the Elisp manual are usually intended to
be _written_ in new code, not merely understood in old code.  I don't
think we should encourage writing code that is harder to understand,
namely requires looking up both default-truncate-lines as well as
truncate-lines for understanding.

-- 
David Kastrup, Kriemhildstr. 15, 44793 Bochum