This will work:
defguard to_boolean(term) when term not in [false, nil]
On Wed, 23 Dec 2020 15:02:43 -0500
Austin Ziegler <halosta...@gmail.com> wrote:
> It would be easy enough to provide this as a predicate in your own
> code if that’s your style preference
>
> ```elixir
> def boolean(falsy) when falsy in [nil, false], do: false
> def boolean(_), do; true
>
> # OR
> def boolean(test), do: if(test, do: true, else: false)
>
> # OR
> def boolean(test), do: !!test
> ```
>
> It can read a little more intentional to say `%{x | assigned?:
> boolean(assigned_to_id)}` than `%{x | assigned?: !!assigned_to_id}`
> or `%{x | assigned?: !is_nil(assigned_to_id)}`, but I don’t really
> think this adds much value to the core.
>
> -a
>
>
>
> On Wed, Dec 23, 2020 at 2:01 PM José Valim <jose.va...@dashbit.co>
> wrote:
>
> > I see. You can match on both or use a with in this case:
> >
> > if membership_ends_on || trial_ends_on || dues_exempt? do
> > changeset
> > else
> > add_error(changeset, :membership_ends_on, "is required")
> > end
> >
> > On Wed, Dec 23, 2020 at 7:50 PM Moxley Stratton
> > <moxley.strat...@gmail.com> wrote:
> >
> >> José:
> >>
> >> I agree on your first example.
> >>
> >> Your second example wouldn't work:
> >>
> >> case membership_ends_on || trial_ends_on || dues_exempt do
> >> nil -> add_error(changeset, :membership_ends_on, "is
> >> required") _ -> changeset
> >> end
> >>
> >> It wouldn't work because `dues_exempt` is a boolean. If
> >> `dues_excempt` is `false`, it wouldn't match the `nil` clause.
> >>
> >> On Wed, Dec 23, 2020 at 10:39 AM José Valim <jose.va...@dashbit.co>
> >> wrote:
> >>
> >>> Thank you for the examples.
> >>>
> >>> However, I believe those examples are not really checking for a
> >>> boolean, but rather for nil. If you don't want to use is_nil, you
> >>> can always compare with nil, which is also pipeable:
> >>>
> >>> def has_access? do
> >>> at_least_logged_in? and get_csrf_cookie(session) != nil
> >>> end
> >>>
> >>> %{event_form | submitted: event_form.submitted_at != nil}
> >>>
> >>> case membership_ends_on || trial_ends_on || dues_exempt do
> >>> nil -> add_error(changeset, :membership_ends_on, "is
> >>> required") _ -> changeset
> >>> end
> >>>
> >>>
> >>> On Wed, Dec 23, 2020 at 7:04 PM Bruce Tate <br...@grox.io> wrote:
> >>>
> >>>> I support this feature. The arguments for
> >>>>
> >>>>
> >>>> - a solution that composes well with pipes and
> >>>> - the linters rejecting the most common solution of !!
> >>>>
> >>>>
> >>>> are all particularly good ones. From my perspective, I teach
> >>>> composition with pipes in the core, `with` in the boundary, and
> >>>> I try to have students return a boolean rather than a truthy
> >>>> result as part of good API design.
> >>>>
> >>>> The inability to convert from truthy to boolean has always felt
> >>>> like a missing feature to me.
> >>>>
> >>>> -bt
> >>>>
> >>>> On Wed, Dec 23, 2020 at 10:42 AM Andrea Leopardi
> >>>> <an.leopa...@gmail.com> wrote:
> >>>>
> >>>>> What's the particular advantage of "to_boolean(term)" over "not
> >>>>> is_nil(term)"? That it supports also booleans, which however
> >>>>> could be used directly in predicates?
> >>>>>
> >>>>> Andrea
> >>>>>
> >>>>> On Wed, Dec 23, 2020 at 4:32 PM Moxley Stratton <
> >>>>> moxley.strat...@gmail.com> wrote:
> >>>>>
> >>>>>> Here are examples:
> >>>>>>
> >>>>>> def has_access? do
> >>>>>> at_least_logged_in? and !!get_csrf_cookie(session)
> >>>>>> end
> >>>>>>
> >>>>>> %{event_form | submitted: !!event_form.submitted_at}
> >>>>>>
> >>>>>> case !!(membership_ends_on || trial_ends_on ||
> >>>>>> dues_exempt) do true -> changeset
> >>>>>> false -> add_error(changeset, :membership_ends_on, "is
> >>>>>> required")
> >>>>>> end
> >>>>>>
> >>>>>> case !!previous_value and !!new_value do
> >>>>>> true -> put_change(changeset, :unconfirmed_email,
> >>>>>> new_value) false -> changeset
> >>>>>> end
> >>>>>>
> >>>>>> submitted? = !!Ecto.Changeset.get_change(changeset,
> >>>>>> :submitted_at)
> >>>>>>
> >>>>>> %{rsvpd: !!participation.rsvpd}
> >>>>>>
> >>>>>> On Tue, Dec 22, 2020 at 11:48 PM José Valim
> >>>>>> <jose.va...@dashbit.co> wrote:
> >>>>>>
> >>>>>>> Can we revisit in which scenarios an explicit boolean
> >>>>>>> conversion is necessary?
> >>>>>>>
> >>>>>>> On Wed, Dec 23, 2020 at 1:21 AM Moxley Stratton <
> >>>>>>> moxley.strat...@gmail.com> wrote:
> >>>>>>>
> >>>>>>>> I would like revisit this issue.
> >>>>>>>>
> >>>>>>>> The issue was last discussed 5 years ago. Much has changed
> >>>>>>>> in that time. The given solution was to use a
> >>>>>>>> double-negative (!!) to convert a given value to a pure
> >>>>>>>> boolean.
> >>>>>>>>
> >>>>>>>> Here are the problems with the suggested solution:
> >>>>>>>> 1. I believe this solution is a hack that is not intuitive to
> >>>>>>>> beginners. It's rarely seen by mid and senior developers,
> >>>>>>>> meaning they have to pause to interpret what !! means.
> >>>>>>>> 2. A double negative can't be part of an Elixir pipeline.
> >>>>>>>> 3. The Credo package warns about double negatives: "Double
> >>>>>>>> boolean negation found". Linters in other languages have a
> >>>>>>>> similar warning. Other languages have a built-in function
> >>>>>>>> (JavaScript has Boolean()) to convert to boolean.
> >>>>>>>> 4. The alternative to double-negative is verbose: "if expr,
> >>>>>>>> do: true, else: false", or the less readable "expr && true
> >>>>>>>> || false"
> >>>>>>>>
> >>>>>>>> I would be happy to submit a PR to add Kernel.to_boolean/1.
> >>>>>>>>
> >>>>>>>> On Sunday, November 1, 2015 at 5:48:28 AM UTC-8 José Valim
> >>>>>>>> wrote:
> >>>>>>>>
> >>>>>>>>> Not necessarily , but the ones in Kernel are. :)
> >>>>>>>>>
> >>>>>>>>> --
> >>>>>>>>>
> >>>>>>>>>
> >>>>>>>>> *José Valim*
> >>>>>>>>> www.plataformatec.com.br
> >>>>>>>>> Skype: jv.ptec
> >>>>>>>>> Founder and Director of R&D
> >>>>>>>>>
> >>>>>>>> --
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> >>>>>>>> .
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> >>>>>> .
> >>>>>>
> >>>>> --
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> >>>>> .
> >>>>>
> >>>>
> >>>>
> >>>> --
> >>>>
> >>>> Regards,
> >>>> Bruce Tate
> >>>> CEO
> >>>>
> >>>>
> >>>> <https://bowtie.mailbutler.io/tracking/hit/f8218219-d2a8-4de4-9fef-1cdde6e723f6/c7c97460-016e-45fb-a4ab-0a70318c7b97>
> >>>>
> >>>> Groxio, LLC.
> >>>> 512.799.9366
> >>>> br...@grox.io
> >>>> grox.io
> >>>>
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> >>>> .
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