AtomicMap

A small utility to convert Elixir maps with mixed string/atom keys to atom-only keyed maps. Optionally with a safe option, to prevent atom space exhaustion of the Erlang VM. Since v0.8 it also supports conversion of keys from CamelCase to under_score format.

AtomicMap can convert simple maps or nested structures such as lists of maps; see Nested Structures below for examples.

Usage

Safety

With no options, it safely converts string keys in maps to atoms, using String.to_existing_atom/1.

iex> AtomicMap.convert(%{"a" => "a", "b" => "b", c: "c"})
%{a: "a", b: "b", c: "c"}

Because safe conversion uses String.to_existing_atom/1, it will raise when the target atom does not exist.

iex> AtomicMap.convert(%{"abcdefg" => "a", "b" => "b"})
** (ArgumentError) argument error
    :erlang.binary_to_existing_atom("abcdefg", :utf8)

To have safe conversion can ignore unsafe keys, leaving them as strings, pass true for the ignore option.

iex> AtomicMap.convert(%{"abcdefg" => "a", "b" => "b"}, %{ignore: true})
%{:b => "b", "abcdefg" => "a"}

To disable safe conversion and allow new atoms to be created, pass false for the safe: option.
(This makes the ignore option irrelevant.)
If the input is user-generated, converting only expected keys will prevent excessive atom creation.

iex> map = %{"expected_key" => "a", "b" => "b", "unexpected_key" => "c"}
%{"expected_key" => "a", "b" => "b", "unexpected_key" => "c"}
iex> filtered_map = Map.take(map, ["expected_key", "b"])
%{"b" => "b", "expected_key" => "a"}
iex> AtomicMap.convert(filtered_map, %{safe: false})
%{b: "b", expected_key: "a"}

Underscoring

By default, "CamelCase" string keys will be converted to under_score atom keys.

iex> AtomicMap.convert(%{ "CamelCase" => "hi" })
** (ArgumentError) argument error
    :erlang.binary_to_existing_atom("camel_case", :utf8)

Note that "camel_case" was the string that failed conversion.
If that atom is explicitly created first, the conversion will succeed.

iex> :camel_case
:camel_case
iex> AtomicMap.convert(%{ "CamelCase" => "hi" })
%{camel_case: "hi"}

Allowing unsafe conversions will also work.
If the input is user-generated, converting only expected keys will prevent excessive atom creation.

iex> map = %{"CamelCase" => "a", "b" => "b", "AnotherCamelCase" => "c"}
%{"CamelCase" => "a", "b" => "b", "AnotherCamelCase" => "c"}
iex> filtered_map = Map.take(map, ["CamelCase", "b"])
%{"b" => "b", "CamelCase" => "a"}
iex> AtomicMap.convert(filtered_map, %{safe: false})
%{b: "b", camel_case: "a"}

Replacing Hyphens

"hyphenated-string" keys will always be converted to under_score atom keys.
There is currently no way to disable this behavior.

iex> AtomicMap.convert(%{"some-key" => "a", "b" => "c"})
** (ArgumentError) argument error
    :erlang.binary_to_existing_atom("some_key", :utf8)

Note that "some_key" was the string that failed conversion.
If that atom is explicitly created first, the conversion will succeed.

iex> :some_key
:some_key
iex> AtomicMap.convert(%{"some-key" => "a", "b" => "c"})
%{b: "c", some_key: "a"}

Allowing unsafe conversions will also work.
If the input is user-generated, converting only expected keys will prevent excessive atom creation.

iex> map = %{"some-key" => "a", "b" => "b", "another-key" => "c"}
%{"some-key" => "a", "b" => "b", "another-key" => "c"}
iex> filtered_map = Map.take(map, ["some-key", "b"])
%{"b" => "b", "some-key" => "a"}
iex> AtomicMap.convert(filtered_map, %{safe: false})
%{b: "b", some_key: "a"}

Nested Structures

# works with nested maps
iex> AtomicMap.convert(%{"a" => 2, "b" => %{"c" => 4}})
%{a: 2, b: %{c: 4}}
# works with nested maps + lists + mixed key types (atoms + binaries)
iex> AtomicMap.convert([ %{"c" => 1}, %{:c => 2}, %{"c" => %{:b => 4}}], %{safe: true})
[%{c: 1}, %{c: 2}, %{c: %{b: 4}}]

Installation

1. Add atomic_map to your list of dependencies in mix.exs:

   def deps do

    [{:atomic_map, "~> 0.8"}]

   end

Todo:

• maybe allow direct conversion to a struct, like Poison does it: as: %SomeStruct{}…

Benchmark

$ mix bench