Ruby notes from Javascript coder

• Symbols begins with :
• function call do not need (), just mention it.
• If you want to get the function object instead of the result of calling it, use method(:function_name), obj.method(:method_name) or class.instance_method(:method_name).
• no curly braces, use `end` key word.
• string enclosed by "" can be perform fancy variable substitute; with '', no substitute.
• substitute: #{variable_name}, #{variable_name.method}
• Inside class, @prop means `this.prop`
• To define class properties: attr_accessor, attr_reader, atter_writer
• Result of the last express in a method definition will be the return value.
• Can define constants by using upper case letter as variable name. It is still mutable, but the interpreter will complain.
• By convention, methods end with ? are predicates, they all return a boolean value.
• By convention, methods end with ! would perform some mutation to the object.
• list.sort => return a new list
• list.sort! => sort the list in place
• Variable naming and their scope:
• begin with $ => global
• begin with @ => instance variable
• begin with @@ => class variable
• begin with [a-z_] => local
• begin with [A-Z] => constant
• Special global variables: $@, $_, $., ..., http://www.tutorialspoint.com/ruby/ruby_predefined_variables.htm
• Function arguments:
• variable length of arguments, (*args), then args will be a Enumerable
• default value def method(a=1, b)
• Operate on collection (Enumerable class): http://ruby-doc.org/core-2.0.0/Enumerable.html, mapping from Javascript Array methods:
• filter <=> select
• reduce <=> reduce, inject
• map <=> map, collect
• every <=> all?
• some <=> any?
• flat_map == collect_concat
• Lambda expression:
• function(x){return x*2;} => {|x| x*2}, do |x| x*2 end
• Ranges:
• (1..10) , double dot, includes 10
• (1...10), triple dot, does not include 10
• JSON like hash syntax works on later version of ruby. But the original syntax looks like:
• my_hash = { :a => 1, "b" => 2, 3 => 3 }
• Array decomposition can be used to pull out values from a array and assign them to variables:
• a, (b, *c), *d = 1, [2, 3, 4], 5, 6
• Support modifier form for if, unless, while, until
• a += 1 if a.zero?
• a += 1 while a < 10
• a += 1 until a > 10
• begin a+= 1 end while a < 10
• Ruby use `next` key word instead of `continue`
• Regex:
• create syntax => same as Javascript:  /[0-9a-z]/i
• re.test( 'some string' ) <=> re === 'some string'