Dextruct

Destructing assignment with <~

It’s so obvious that pattern matching with = is just awesome. But less then occasionally, we still want some destructing assignment, witout MatchError, works like in other languge. Dextruct library provides a <~ operator which imitates similar behavior, with some other goodies.

Installation

The package can be installed by adding dextruct to your list of dependencies in mix.exs:

def deps do
  [
    {:dextruct, "~> 1.0.0"}
  ]
end

After excute mix deps.get command, add use Dextruct in your module:

def YourModule do
  use Dextruct
end

Destruct assignment

The <~ operator works on two senarios, List and Map.

List

For destructing assignment on List, it simply fills up the list on left hand side with filler (nil by default).

iex> [a, b, c] <~ [1, 2]
[1, 2, nil]

iex> c
nil

One of the useful example is use with Regex‘s optional group matching. Originally it will omit the unmatched groups in the end.

iex> Regex.run(~r/(a)?(b)?(c)?(d)?/, "ab")
["ab", "a", "b"]

iex> [matched, a, b, c, d] <~ Regex.run(~r/(a)?(b)?(c)?(d)?/, "ab")
["ab", "a", "b", nil, nil]

Map

Destructing assignment on Map, then as well, fill the keys missing in the right hand side map, with filler.

iex> %{a: a, b: b, c: c} <~ %{a: 1}
iex> a
1
iex> b
nil
iex> c
nil

Different filler

You can specify the filler by fill option while use Dextruct. That means you can only have one filler for each module.

def YourModule do
  use Dextruct, fill: 0
end

Map short-hand literal

Dextractor also come with a short-hand literal for Map, which is sigil_m.

iex> ~m{a, b, c: foo} = %{a: 1, b: 2, c: 3}
%{a: 1, b: 2, c: 3}

It works well with <~, of course.

iex> ~m{a, b, c: foo} <~ %{a: 1}
iex> a
1
iex> b
nil
iex> foo
nil

Exclude sigil_m

To be honest, if you use shorthand map literal quite often, without change the binding variable in between, i.e., c: foo in the previous code demo, you should consider using ShortMaps instead. Which is more like the consensus of the community for now.

To do so, you’ll like to except the sigil_m while using Dextruct.

defmodule YourModule do
  use Dextruct, except: [sigil_m: 2]
end

Actually, the sigil_m comes with Dextruct will be exclude by default or even deprecate, once the ShortMap literal becomes the de facto standard anytime in the future.

Is it any good?

Hopefully.

License

Apache 2