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Info Chapter 8 ■ Objects Object Metadata As with other data types within Ruby, we can easily determine some metadata regarding an object, such as the Class that it is part of, details about the object, or the methods available. instance_of? is_a? Car #=> true We can determine the available methods within a class. methods #=> startEngine nil? ~ eql? private_methods puts "=======================" puts "" #=> Public Methods startEngine nil? ~ eql? trimmed ... ======================= Protected Methods ======================= Private Methods initialize_copy initialize_dup initialize_clone sprintf ...

Has_key? has_value? has_value? 1 :002 > score["Joe Bloggs"] => 10 Hashes are commonly used when passing named parameters into a method, where the number and order of parameters can differ depending on what is required. With using a traditional set of parameters, nil or empty data would have to be passed during the method call, and filtered out later; instead a hash can be used. If a hash is used as the last parameter to a method, no braces are required either. select{|type,quantity| quantity > 5 } => {:books=>25, :cds=>7} Looping Through Hashes At times, we need to loop through hashes rather than retrieving individual elements, to do this utilize the each method.

While the name sounds like this is a loop, this is in fact an iterator method. First, we will set up the simplest type of loop, the infinite loop, printing out Hello World on a new line forever. /usr/bin/env ruby loop do puts "Hello World" end #=> Hello World Hello World Hello World Hello World ... However, this type of loop is not very useful, as this would continue running forever. Instead we could use a break, next, or redo keyword to alter the running of the loop. First we will use the break keyword, which allows us to exit the loop.