This is an interesting idea, but maybe `then/2` (or case/2 if you're fine
piping in it) could already cover these cases quite well (equivalent to
your pattern_filter! function):
"$3.45" |> then(fn "$" <> money -> money end) |> String.to_float()
"$3.45" |> case do "$" <> money -> money end |> String.to_float()
The non-raising alternative might be slightly more verbose because you need
a second clause. But most of the time (like your money example), the next
step of the pipe might fail on nil anyway. Or maybe a with/1 pipeline might
work better than the pipe operator if you want a succession of happy-path
matches?
If we move forward, it might be better to explicitly declare the returned
expression, not just infer it from dangling variables: it isn't obvious
what should `{a, b}` or `{a, b, a}` return. Something like:
{1, 2, 1} |> pattern_filter(b <- {a, b, a})
Le mer. 14 déc. 2022 à 05:50, 'Matt Farabaugh' via elixir-lang-core <
elixir-lang-core@googlegroups.com> a écrit :
> All,
>
> I wrote a macro which allows for using a pattern to essentially extract a
> value from a data structure:
>
>
> @doc """
> Filter a value out of data using a pattern with one variable. Returns a
> default value
> if no match. Raises if pattern contains no variables or more than one
> variable.
>
> ## Examples
>
> iex> "$3.45" |> PatternHelpers.pattern_filter("$" <> money) |>
> String.to_float()
> 3.45
>
> iex> {1,2,3} |> PatternHelpers.pattern_filter({1,_,a})
> 3
>
> iex> %{a: 1, b: 2} |> PatternHelpers.pattern_filter(%{a: 9, b: b})
> nil
>
> iex> %{a: 1, b: 2} |> PatternHelpers.pattern_filter(%{a: 9, b: b}, "???")
> "???"
> """
>
> And an unsafe version:
>
> @doc """
> See `pattern_filter/3`. Raises if no match.
>
> ## Examples
>
> iex> {1,2,3} |> PatternHelpers.pattern_filter!({9,_,b})
> ** (MatchError) no match of right hand side value: {1, 2, 3}
> """
>
> This is my first proposal. Please let me know if this idea is worth some
> attention, and how I might better do my part to present it. I have code
> obviously but I'm not sure this is the place for it.
>
> Thanks,
> Matt F
>
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