I've started looking at Access.at(index, default \\ nil).
I guess it's fine for
list = [%{name: "john"}, %{name: "mary"}]
assert get_in(list, [Access.at(10, :my_default), :name])
to give a FunctionClauseError, since it ends up calling
Access.get(:my_default, :name, nil)
? Or should this situation be handled more gracefully? If so, how?
On Mon, Jul 6, 2020 at 11:58 AM Henrik Nyh <[email protected]> wrote:
> Great, thanks! Will try my hand at a PR :)
> On 6 Jul 2020, 11:58 +0100, José Valim <[email protected]>, wrote:
>
> Sounds good to me. Adding new bang variants are relatively
> straight-forward. Can you please send a PR? Also, for consistency reasons,
> can you please change Access.at/1 to become Access.at(index, default \\
> nil)?
>
> Thank you!
>
> On Mon, Jul 6, 2020 at 12:40 PM Henrik N <[email protected]> wrote:
>
>> Hi,
>>
>> I propose adding an `Access.at!` that raises when the given index is out
>> of bounds, analogous to `Access.key!`.
>>
>> The current `Access.at` is not nil safe as discussed in
>> https://groups.google.com/g/elixir-lang-core/c/CvdW1FsvSf0/m/nlvxkThuEwAJ,
>> but it's also not analogous to `Access.key!`.
>>
>> I specifically want it to raise and point to being out of range (or
>> whatever the terminology is), rather than causing nil errors further down
>> the line.
>>
>> Current behaviour with `Access.at`:
>>
>> # Happy case. Everything exists.
>> iex(20)> get_in([%{key: "value"}], [Access.at(0), :key])
>> "value"
>>
>> # Nil safe when index is out of bounds.
>> iex(21)> get_in([%{key: "value"}], [Access.at(1), :key])
>> nil
>>
>> # Not nil safe, but error doesn't point to the array index.
>> iex(22)> get_in([%{key: "value"}], [Access.at(1), Access.key!(:key)])
>> ** (RuntimeError) Access.key!/1 expected a map/struct, got: nil
>> (elixir 1.10.3) lib/access.ex:514: anonymous fn/4 in Access.key!/1
>>
>> I propose something like this behaviour, with `Access.at!`:
>>
>> # Happy case – behaves the same.
>> iex(20)> get_in([%{key: "value"}], [Access.at!(0), :key])
>> "value"
>>
>> # Explodes.
>> iex(21)> get_in([%{key: "value"}], [Access.at!(1), :key])
>> ** (FooError) index 1 not found in: [%{key: "value"}]. Its highest index
>> is 0.
>>
>> # Explodes in the same way.
>> iex(22)> get_in([%{key: "value"}], [Access.at(1), Access.key!(:key)])
>> ** (FooError) index 1 not found in: [%{key: "value"}]. Its highest index
>> is 0.
>>
>> What do you think?
>>
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