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FirstExisting

FirstExisting is an extremely simple Ruby gem that contains methods for selecting objects based on their existence.

Installation

Add this line to your application's Gemfile:

gem 'first_existing'

And then execute:

$ bundle install

Or install it yourself as:

$ gem install first_existing

Usage

FirstExisting is currently composed of only 3 methods: first_existing, Hash#required!, and Hash#default!

first_existing

first_existing accepts list of objects, returning that first that is not nil. It is automatically added globally to Kernel. Example:

first_existing(nil, nil, "test", nil) # => "test"

A common use case for it is with Ruby on Rails content helpers, like so:

<head>
  <title><%= first_existing(content_for(:title), "default") %></title>
</head>

Hash#required!

FirstExisting also automatically adds a required! method to Hash that automatically raises exceptions when the given key does not exist. For example:

def some_method(options = {})
  options.required! :name
  "Hello, #{name}"
end

some_method(name: "Jacob") # => "Hello, Jacob"
some_method(last_name: "Lockard") # => RuntimeError (The 'name' option is required!)

Hash#default!

Finally, a default! method is added to Hash that automatically sets defaults for a key if its value is nil. It accepts as parameters the name of the key to change and a list of default values. The first existing value is used. For example:

$GLOBAL_LAST_NAME = "Global"
class Example
    def initialize(last_name:)
      @last_name = last_name
    end

    def some_method(options = {})
      options.default! :name, "Jacob"
      options.default! :last_name, $GLOBAL_LAST_NAME, @last_name, "Lockard"
      "Hello, #{options[:name]} #{options[:last_name]}"
    end
end

Example.new(last_name: "Class").some_method(last_name: "Last") # => "Hello, Jacob Last"

Example.new(last_name: "Class").some_method(name: "First") # => "Hello, First Global"

$GLOBAL_LAST_NAME = nil
Example.new(last_name: "Class").some_method # => "Hello, Jacob Class"

Example.new(last_name: nil).some_method # => "Hello, Jacob Lockard"