> What I find curious is that once we implement Kernel.nillable_get_in, why
would anyone choose to use Kernel.get_in instead?
When I don't expect anything to be nil, I want it to fail as soon as
possible, instead of having nil further creeping into the system.
Personally, most of the times I used get_in and friends, I am working with
structured data (the opposite of your use case). If any nil shows up, it
should be an error.
And changing get_in may not break code, expectations I had when I wrote the
code would certainly be broken. And I would personally be unhappy if we
simply changed get_in without introducing an option to write assertive
code. Writing assertive code is an important of Elixir. It is why we have
map.foo in addition to map[:foo]. So I think it is best to remove changing
get_in from the discussion altogether, I don't see it happening.
We can continue discussing alternatives though.
On Sat, Feb 8, 2020 at 1:47 AM Greg Vaughn <gvau...@gmail.com> wrote:
> One more point. Even if my proposal is not accepted, these docs for
> Kernel.get_in really need to change
>
> In case any of the entries in the middle returns nil, nil will be returned
> as
> per the Access module:
>
> iex> users = %{"john" => %{age: 27}, "meg" => %{age: 23}}
> iex> get_in(users, ["unknown", :age])
> nil
>
> The Access module guarantees no nil-safety. It's an "accident" that
> Access.get does.
>
> -Greg Vaughn
>
>
> > On Feb 7, 2020, at 4:40 PM, José Valim <jose.va...@dashbit.co> wrote:
> >
> > Hi Greg, I have been thinking more about this too, and I think there are
> some neat ways we can make this more accessible:
> >
> > We could introduce Access.nillable (please suggest a better name) that
> you would use like this:
> >
> > get_in(root, Access.nillable([:foo, :bar, Access.at(0)]))
> >
> > Basically, it traverses the path and sets all functions in the path to
> something that handles nil. In your apps, you can quickly encapsulate it
> like this:
> >
> > nillable_get_in(root, [:foo, :bar, Access.at(0)])
> >
> > It is concise, backwards compatible, and clear in intent.
> >
> > Thoughts?
> >
> > On Fri, Feb 7, 2020 at 11:35 PM Greg Vaughn <gvau...@gmail.com> wrote:
> > I just wanted to follow up and summarize here. I submitted a PR
> https://github.com/elixir-lang/elixir/pull/9773 with some more
> discussion, but the core point there was that we needed more discussion on
> the core list before a PR and it was closed. Nil-safety by default is
> undesirable in more Access functions than Access.get.
> >
> > I'm exploring this on my own in my own codebase as I rework all the
> get_in calls I assumed were nil safe despite using Access.at. I am quite
> against a solution that is more verbose to gain mil safety as I use this at
> the edges of my system in an anti-corruption-layer. I'd rather see this
> implemented once, well, in the standard library than expect thousands of
> projects to do it themselves or bring in a 3rd party solutions to achieve
> it.
> >
> > Feel free to discuss some more.
> >
> > -Greg
> >
> > > On Jan 30, 2020, at 12:02 PM, Allen Madsen <allen.c.mad...@gmail.com>
> wrote:
> > >
> > > I'm in favor of them being nilsafe by default.
> > >
> > > Allen Madsen
> > > http://www.allenmadsen.com
> > >
> > >
> > > On Wed, Jan 29, 2020 at 11:24 AM Tor Bjornrud <bjorn...@gmail.com>
> wrote:
> > > I wouldn't mind having opts for something like this. Avoids creating
> a slew of Access functions that then become difficult to sift through.
> > >
> > > %{"items" => nil} |> get_in(["items", Access.at(0, nilsafe: true)
> > >
> > > On Tuesday, January 28, 2020 at 8:10:04 PM UTC-6, Greg Vaughn wrote:
> > > Thanks, José. I agree with the need to be consistent. I will look at
> the bigger picture, though, like Manfred I find the addition of "maybe" to
> be awkward, so my preference is to have the existing recommended functions
> in the Access module intended for use with get_in to be consistently nil
> safe. I'm open to more ideas, too.
> > >
> > > -Greg Vaughn
> > >
> > > > On Jan 28, 2020, at 12:45 PM, José Valim <jose...@dashbit.co>
> wrote:
> > > >
> > > > The proposal is reasonable however it would introduce an
> inconsistency since the other selectors in Access, such as Access.key, are
> also not nil safe. So whatever solution we choose needs to be consistent.
> > > >
> > > > One possible suggestion is to introduce a "Access.maybe" that
> composes but composition would have to be back to front:
> > > >
> > > > %{"items" => nil} |> get_in(["items", Access.at(0) |> Access.maybe])
> > > >
> > > > Another idea is to introduce maybe_at, maybe_key, maybe_key! and so
> on. But I am not sure if this is desirable. Thoughts?
> > > >
> > > > On Tue, Jan 28, 2020 at 7:33 PM Greg Vaughn <gva...@gmail.com>
> wrote:
> > > > I propose that the function returned from Access.at/1 special case
> nil such that the overall Kernel.get_in/2 call returns nil instead of
> raising an error.
> > > >
> > > > Rationale:
> > > > I originally blamed this on Kernel.get_in/2 and I'd like to thank
> Eric Meadows-Jönsson for explaining the underlying reason to me on Slack.
> > > >
> > > > I like to think of Kernel.get_in/2 as a nil-safe way of plucking
> values out of nested data structures, but I learned today that is only
> partially correct. The nil-safety comes from the underlying Access.get/2
> calls. The docs for get_in includes:
> > > >
> > > > In case any of the entries in the middle returns nil, nil will be
> returned as per the Access module:
> > > > iex> users = %{"john" => %{age: 27}, "meg" => %{age: 23}}
> > > > iex> get_in(users, ["unknown", :age])
> > > > nil
> > > >
> > > > and I expected use of Access.at/1 in my keys to act similarly, but
> it doesn't. For example:
> > > >
> > > > iex(185)> %{"items" => ["desired_value"]} |> get_in(["items",
> Access.at(0)])
> > > > "desired_value"
> > > > iex(186)> %{"items" => nil} |> get_in(["items", Access.at(0)])
> > > > ** (RuntimeError) Access.at/1 expected a list, got: nil
> > > > (elixir) lib/access.ex:663: Access.at/4
> > > >
> > > > I propose that the function returned from Access.at/1 special case
> nil such that the overall get_in/2 call returns nil instead of raising an
> error. I have not dug into the source yet but I'm happy to work up a PR if
> there is interest in this change.
> > > >
> > > > -Greg Vaughn
> > > >
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