first_arr = []
secnd_arr = [5,7,-11,"some_string",:some_symbol]
third_arr = [:some_symbol,[:other_symbol,"some_string"],[],123]

$> first_arr[0]
 => nil 
$> first_arr[1457]
 => nil 
$> secnd_arr[3]
 => "some_string" 
$> secnd_arr[184]
 => nil 
$> third_arr[0]
 => :some_symbol 
$> third_arr[1]
 => [:other_symbol, "some_string"] 
$> third_arr[1][0]
 => :other_symbol 
$> third_arr[-1]	  # access last element
 => 123 
$> third_arr[-2]
 => [] 

$> third_arr[1][0] = "whatever"
 => "whatever" 

some_function(secnd_arr).other_function{|x| x.kind == :some_symbol}.map{|x| x.is_a?(Numeric)}

some_hash = {:elem1 => 123, :elem2 => "xyz"}
$> some_hash[:elem2]
 => "xyz"