ShorterMaps

~M sigil for map shorthand. ~M{a} ~> %{a: a}

Motivation

Code like %{id: id, name: name, address: address} occurs with high frequency in many programming languages. In Elixir, additional uses occur as we pattern match to destructure existing maps.

ES6 (ES2015 for those folks who insist on proper names) provided javascript with a shorthand to create maps with keys inferred by variable names, and allowed destructuring those maps into variables named for the keys. ShorterMaps provides that functionality to Elixir.

Credits

ShorterMaps adds additional features to the original project, ShortMaps, located here. The reasons for the divergence are summarized here.

The key syntactic difference is motivated by the trailing a in ~m{}a. To maintain backward compatibility, that syntax still works, but ShorterMaps adds a ~M sigil that defaults to the a modifier.

Basic Usage

Note: you must import ShorterMaps for the sigil to work.

Pattern Matching / Function Heads

iex> import ShorterMaps
...> ~M{foo bar baz} = %{foo: 1, bar: 2, baz: 3}
...> foo
1
...>
...> defmodule MyMod do
...>   def extract_id(~M{id} = args), do: id
...> end
...> MyMod.extract_id(%{id: 5, name: "Chris"})
5

end

Map Construction

iex> import ShorterMaps
...> name = "Meg"
...> ~M{name} # M = atom keys
%{name: "Meg"}
...> ~m{name} # m = String keys
%{"name" => "Meg"}

Structs

The first word inside the sigil must be '%' followed by the module name:

iex> import ShorterMaps
...> defmodule MyStruct do
...>   defstruct [id: 0, name: ""]
...> end
...>
...> # Struct construction:
...> id = 5
...> name = "Chris"
...> ~M{%MyStruct id name}
%MyStruct{id: 5, name: "Chris"}
...>
...> # Pattern Matching:
...> ~M{%MyStruct id} = %MyStruct{id: 1, name: "Bob"}
...> id
1

Variable Pinning

iex> import ShorterMaps
...> name = "Meg"
...> ~M{^name} = %{name: "Meg"}
%{name: "Meg"}
...> ~M{^name} = %{name: "Megan"}
** (MatchError) no match of right hand side value: %{name: "Megan"}

Variable Ignore

Useful for pattern matching against the structure of a map but don't need all of the variables.

iex> import ShorterMaps
...> ~M{_foo bar} = %{foo: "bar", bar: "foo"}
%{bar: "foo", foo: "bar"}
...> bar
"foo"
...> foo
** (CompileError) iex:4: undefined function foo/0

You can see more examples in the docs for the sigil_M/sigil_m macros.

Installation

# mix.exs

defp deps do
  [
    {:shorter_maps, "~> 1.1"},
  ]
end