Despite typically being a "put it in the standard library" guy, I don't think
that `then_if` actually composes as well as it looks like it does on the tin
due to the fact that `then` is often used in pipelines, where some
transformation has happened and you want to check a condition *on that result*.
For example:
```elixir
changeset
|> do_some_checking()
|> then_if(<is_valid>, &do_more/1)
```
I think that `then` is kind of "already" the composition tool that we need for
expressive pipes.
```elixir
changeset
|> do_some_checking()
|> then(fn changeset ->
If changeset.valid do
do_more(changeset)
else
changeset
end
end)
```
I can see an argument that it is very verbose, but its also about as flexible
as it can get. My suggestion would be to, if added, have `then_if` take a
function as its first argument.
```elixir
changeset
|> do_some_checking()
|> then_if(&(&1.valid?), &do_more/1)
```
> On Dec 6, 2024, at 10:30 AM, Ben Wilson <benwilson...@gmail.com> wrote:
>
> Exploring what that looks concretely in this case:
>
> ```
> map
> |> other_stuff
> |> then_if(opts[:foo], &Map.put(&1, :key, value))
> ```
>
> I like it! Conditional map insert helper functions are definitely something
> we've written over and over again in our code bases and while it's easy to
> do, I think in some cases this is cleaner looking than a proliferation of
> `maybe_put_foo` functions.
>
> - Ben
>
> On Friday, December 6, 2024 at 9:59:40 AM UTC-5 José Valim wrote:
>> Hi Juan!
>>
>> My initial gut feeling is that this approach does not scale. What if you
>> want to delete a key conditionally? Should we have delete_if?
>>
>> It feels a more general approach would be to introduce `then_if`:
>>
>> then_if(subject, condition?, function)
>>
>> Or similar. :)
>>
>> José Valim
>> https://dashbit.co/
>>
>>
>> On Fri, Dec 6, 2024 at 3:27 PM Juan Manuel Azambuja <ju...@mimiquate.com <>>
>> wrote:
>>> Hello,
>>>
>>> After working with Elixir for some time I have found myself repeating some
>>> patterns when dealing with maps.
>>>
>>> One pattern I see repeated constantly in different apps developed by myself
>>> or others is adding values to a map conditionally or returning the map
>>> unchanged. This comes in different flavors:
>>>
>>>
>>> or
>>>
>>>
>>> When this pattern gets used enough in an app, it's normal to see it
>>> abstracted in a MapUtils module that updates the map conditionally if a
>>> condition is met or returns the map unchanged otherwise.
>>>
>>> My proposal is to include Map.put_if/4 which would abstract the condition
>>> check and return the map unchanged if the condition is not met:
>>>
>>>
>>>
>>> Enhancing the API by doing this will result in less code and more readable
>>> solutions.
>>>
>>> Thanks for reading!
>>>
>>
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