Add json encoding

lib/quantity.ex

@@ -146,7 +146,7 @@ defmodule Quantity do
 
   @doc """
   Encodes the quantity as a string. The result is parsable with parse/1
-  If the exponent is positive, encode usinge the "raw" format to preserve precision
+  If the exponent is positive, encode using the "raw" format to preserve precision
 
   iex> Quantity.new(42, -1, "db") |> Quantity.to_string()
   "4.2 db"
@@ -351,6 +351,15 @@ defmodule Quantity do
     end
   end
 
+  defimpl Jason.Encoder do
+    @impl Jason.Encoder
+    def encode(value, opts) do
+      value
+      |> Quantity.to_string()
+      |> Jason.Encode.string(opts)
+    end
+  end
+
   # Normalizes unit to a standard form:
   # * Shorten unit as much as possible
   # * At most one :div (with possibly many :mults on each side)

mix.exs

@@ -36,6 +36,7 @@ defmodule Quantity.MixProject do
     [
       # Decimal
       {:decimal, "~> 2.0"},
+      {:jason, "~> 1.4"},
 
       # Documentation
       {:ex_doc, "~> 0.21", only: :dev, runtime: false},

test/quantity_test.exs

@@ -55,6 +55,10 @@ defmodule QuantityTest do
     assert Quantity.to_string(~Q[42]) == "42"
   end
 
+  test "encode to json from map" do
+    assert %{quantity: ~Q[12.45 DKK]} |> Jason.encode!() == ~S|{"quantity":"12.45 DKK"}|
+  end
+
   test "for non-number decimals" do
     ["inf", "-inf", "nan"]
     |> Enum.each(fn not_number ->