TinyMaps

A successor to the shorter_maps package.

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

Getting started

1. Add {:tiny_maps, "~> 3.0"}, to your mix deps
2. Add import TinyMaps to the top of your module
3. DRY up your maps and structs with ~M and ~m. Instead of %{name: name} use ~M{name}, and for %{"name" => name} use ~m{name}. When the key and the variable don't match, don't fret: ~M{name, id: current_id} expands to %{name: name, id: current_id}.

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 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. TinyMaps provides that functionality to Elixir.

Syntax:

~M and ~m can be used to replace maps anywhere in your code. The TinyMaps sigil syntax operates just like a vanilla elixir map, with two main differences:

1. When a variable name stands alone, it is replaced with a key-value pair, where the key is the variable name as a string (~m) or an atom (~M). The value will be the variable. For example, ~M{name, id: get_free_id()} expands to %{name: name, id: get_free_id()}.

2. Struct names are enclosed in the sigil, rather than outside, e.g.: ~M{%StructName key, key2} === %StructName{key: key, key2: key2}. The struct name must be followed by a space, and then comma-separated keys. Structs can be updated just like maps: ~M{%StructName old_struct|key_to_update}

Examples

iex> import TinyMaps
...> name = "Chris"
...> id = 6
...> ~M{name, id}
%{name: "Chris", id: 6}

# It's ok to mix in other expressions:
...> ~M{name, id: id + 200}
%{name: "Chris", id: 206}

# or even nest the sigil (note the change in delimiters to paren):
...> ~M{name, id, extra_copy: ~M(name, id)}
%{name: "Chris", id: 6, extra_copy: %{name: "Chris", id: 6}}

# We can use String keys:
...> ~m{name, id}
%{"name" => "Chris", "id" => 6}

# And we can update existing maps:
...> map_1 = %{name: "Bob", id: 9}
...> ~M{map_1|name}
%{name: "Chris", id: 9}

# Struct syntax is a little funky:
...> defmodule MyStruct do
...>   defstruct [id: nil, name: :default]
...> end
...> ~M{%MyStruct id}
%MyStruct{id: 6, name: :default}

# Structs can be updated too:
...> initial_struct = %MyStruct{name: "Chris", id: :unknown}
...> ~M{%MyStruct initial_struct|id}
%MyStruct{name: "Chris", id: 6}

# Because the expansion happens at compile time, they can be used __anywhere__:

# in function heads:
...> defmodule MyModule do
...>   def my_func(~M{name, _id}), do: {:id_present, name}
...>   def my_func(~M{name}), do: {:no_id, name}
...> end

# in pattern matches:
...> ~M{age, model} = %{age: -30, model: "Delorean", manufacturer: "AMC"}
...> age
-30

Credits

TinyMaps is continuation of the ShorterMaps which has become unmaintained and I have not been able to make contact with the maintainer.

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

Quick Reference:

• Atom keys: ~M{a, b} => %{a: a, b: b}
• String keys: ~m{a, b} => %{"a" => a, "b" => b}
• Structs: ~M{%Person id, name} => %Person{id: id, name: name}
• Pinned variables: ~M{^a, b} => %{a: ^a, b: b}
• Ignore matching: ~M{_a, b} => %{a: _a, b: b}
• Map update (strings or atoms): ~M{old|a, b, c} => %{old|a: a, b: b, c: c}
• Struct update: ~M{%Person old_struct|name} => %Person{old_struct|name: name}
• Mixed mode: ~M{a, b: b_alt} => %{a: a, b: b_alt}
• Expressions: ~M{a, b: a + 1} => %{a: a, b: a + 1}
• Zero-arity: ~M{a, b()} => %{a: a, b: b()}
• Modifiers: ~m{blah}a == ~M{blah} or ~M{blah}s == ~m{blah}

Note: you must import TinyMaps for the sigils to work.