Keyword Lists and Defaults

Account.balance(transactions)

Passing options with keyword lists

Account.balance(..., currency: "dollar", symbol: "$:)

And this is same as

Account.balance(..., [{:currency, "dollar"}, {:symbol, "$"}])

Reading Keyword Lists

defmodule Account do

    def balance(transactions, options) do
        currency = options[:currency]
        symbol = options[:symbol]

        balance = calculate_balance(transactions)
        "Balance in #{currency}: #{symbol}#{balance}"
    end
    ...
end

Account.balance(transactions, currency: "dollar", symbol: "$")

Must Pass All Arguments

defmodule Account do
    def balance(transactions, options \\ []) do
        currency = options[:currency]
        symbol = options[:symbol]
        ...
    end
    ...
end

With default values

Account.balance(transactions)

 defmodule Account do
    def balance(transactions, options \\ []) do
        currency = options[:currency] || "dollar"
        symbol = options[:symbol] || "$"
        ...
    end
    ...
end

Account.balance(transactions)

Example of Library in Elixer

• https://github.com/elixir-ecto/ecto

Repo.all(from u in User, where: u.age > 21, where: u.is_active == true)