Re: add-hook and defvar

[Robin Templeton]

Artur Malabarba <address@hidden> writes:

> While it's nice that `add-hook' tries to do the right thing even when
> the variable isn't defined yet, that's a bit of a false assurance.
> Although it's documented in the docstring, it seems undesirable that
> it sets the variable. This means that if the hook's defvar were to
> specify an initial value, this value won't take effect because of that
> preceding `add-hook' invocation.

This seems like a bug in the program defining the hook variable, not a
problem with `add-hook' per se; programs should always allow for the
possibility that the user has set their own value for a variable and
that the default value in the defvar form is ignored. I would expect the
program to call `add-hook' itself if the default hook functions were
important.

> In this situation, add-hook doesn't so much "add" as it actually sets
> the value of the hook.
>
> The following patch is one way of having `add-hook' always add,
> without overriding the "future" initial value of the hook. It is not
> complete, it's intended as a possible outline (hopefully a
> conversation starter).
>
> The big disadvantage is that it's not backwards compatible. Any code
> out there that relies on the variable being set by `add-hook' will
> break.
> There's also the disadvantage that it adds a symbol-property check to
> every `defvar' call.
>
> Any thoughts?

Another potential problem is that `add-hook' followed by `run-hooks'
will do nothing if the hook variable has not been defined. If the
behavior of `add-hook' were changed, I would prefer it if it simply
required the variable to be defined; that would avoid the above
disadvantages, would make it consistent with functions like
`add-to-list', and would normally ensure that the hook is initialized as
expected.

my 2¢,
robin
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