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 <[email protected]
> <javascript:>> 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 <[email protected]
> <javascript:>> 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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