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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>>>>>>>> To view this discussion on the web visit
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>>>>>>>> <https://groups.google.com/d/msgid/elixir-lang-core/45dc9a7b-1657-4d02-933b-fe8fe182c2bcn%40googlegroups.com?utm_medium=email&utm_source=footer>
>>>>>>>> .
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>>>>> --
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>>>>> To view this discussion on the web visit
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>>>>> <https://groups.google.com/d/msgid/elixir-lang-core/CAM9Rf%2BLMgPAwYN8FyEs0t%3DVvmAQzP9gx-VjykT6Q11Dvd%3DsVyA%40mail.gmail.com?utm_medium=email&utm_source=footer>
>>>>> .
>>>>>
>>>>
>>>>
>>>> --
>>>>
>>>> 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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>>>> <https://groups.google.com/d/msgid/elixir-lang-core/CAFXvW-47q8nXAKw%2B8ZH_NHh2booBmEYtDf-dB70GHXPDXnZmXw%40mail.gmail.com?utm_medium=email&utm_source=footer>
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--
Austin Ziegler • halosta...@gmail.com • aus...@halostatue.ca
http://www.halostatue.ca/ • http://twitter.com/halostatue
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