Setting Defaults in Ruby
Let’s start out with a plain old method.
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def hello puts "Hi!" end |
Now let’s un-hardcode that string in the puts by adding a parameter.
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def hello(greeting="Hi!") puts greeting end >> hello Hi! >> hello("Hola!") Hola! |
Great. We have a default String. But what about something more complex. What if we want a hash of options. Say we have a little piece of an IRC client.
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def connect(options={}) defaults = { :server => "irc.freenode.net" } options = defaults.merge(options) puts "Connecting to #{options[:server]} ..." end <pre lang="ruby"> Now when we use it like this, we can connect to a default server or override it. <pre lang="ruby"> >> connect Connecting to irc.freenode.net ... >> connect({:server => "irc.efnet.net"}) Connecting to irc.efnet.net ... |
Now a more complicated example. All we’re doing here is loading defaults from a YAML file and doing the same thing as before.
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require 'yaml' class Preferences def initialize if !File.exists?("preferences.yml") # example file options = {:server => "irc.efnet.net"} self.save!(options) end @values = YAML::load(File.open("preferences.yml")) end def to_hash @values end def save!(options) preferences = File.open("preferences.yml", "w") do |f| f.write(options.to_yaml) end end end def connect(options={}) defaults = { :server => "irc.freenode.net", :username => "CHANGE-USER-NAME, see README.txt", :channel => "#chat" } options = defaults.merge(options) puts "Connecting to #{options[:server]} as #{options[:username]}..." end # Main prefs = Preferences.new options = {:channel => "#meow"} connect(prefs.to_hash) options[:username] = "Bob" options[:server] = "irc.efnet.net" prefs.save!(options) |
Go ahead and give it a try and play with it. It’s a good recipe with many uses.