FirstExisting is an extremely simple Ruby gem that contains methods for selecting objects based on their existence.
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
FirstExisting is currently composed of only 3 methods: first_existing, Hash#required!, and Hash#default!
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>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!)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"