Not being familar with ruby, here's a few notes / cheat sheet as I keep forgetting the basics
Functions:
def name (param1="Default Value", paramN, *args, &block)
// actions
return val
end
*args - A variable sized argument (arg.length)
&block - a block to be automatically converted to Proc
Naming conventions:
| Type |
Example |
Notes |
| constant |
Pi |
Starts with capital letter. Is mutable!!! |
| boolean test |
isEql? |
Methods with a boolean response are prepended with a '?' |
| destructive test |
delete! |
Makes changes to object on which the function is invoked on (ends with '!') |
| setter method |
name=(n) |
method name ends in '='s sign |
| instance variable |
@counter |
. |
| class variable |
@@times |
. |
| global variables |
$global |
. |
Symbols:
Placeholders for identifiers and strings, always prefixed by a ':' (colon). Can't be directly created - for Strings - use to_sym or intern methods, use id2name to transform back.
Effectively transforms the string content into a label. Because of the interning symbols are more memory efficient then copies of strings.
name = "Matz"
name.to_sym # => :Matz
:Matz.id2name # => "Matz"
name == :Matz.id2name # => true
Conditionals:
if a == b then <do stuff> end
if a == b: <do stuff> end // : instead of 'then'
if a == b && b == c: <do stuff> end
puts "output" if a == b // no need for then & end if used as a statement modifier
if a == 1
puts 'one'
elsif a == 2
puts 'two'
else
puts '!(1 || 2)'
end
if a == :foo
puts "test against symbol multi-line"
elsif a == :bar: puts "test against symbol single line (extra colon)"
end
case foo
when :foo; "Foo" // NOTE: the ':' operator was allowed in ruby 1.8
when 1..3; "Range of value test"
else "default"
end
Iteration:
while <condition> do // 'do' is optional
// code
end
begin
// code
end while <condition>
for i in 1..5 do // 'do' is optional
print i, " "
end
// Alternatively, use 'times' method from the Integer class
5.times { |i| print i, " " }
// also there is upto and downto methods
2.upto(8) { |i| print i, " " }
unless - like a negated if statement
until - like a while loop, do until a condition is met
loop - creates a loop forever until a break condition is met (such as break statement)
Strings:
my_string = %{A string with customer delimiters defining start / end}
multi_line = <<# // use -<< to keep indentation
text across multiple
lines with a custom delimiter
#
h = "Foo -".concat("bar") << "!" // concatenation methods
h.freeze // make string immutable, check with frozen? method
h[3] // access 3rd character code at index location (use h[3].chr for character)
h[start, len] // substring
h.index("b") // search for char
"a" <=> "a" // 'spaceship operator' contains character code of strings, returns 0, 1 or -1
== and eql? are slightly different(== returns true if two objects are Strings, eql? checks content and length)
Arrays:
Array.new || Array.new(12) || Array.new 12 || Array.new(12, <default>)
Array.new(10) { |e| e = e * 2 } // [0, 2, 4, ..., 18 ]
%w{ foo bar who har } // new array with whitespace separating entries
rg = Array(0..9) // [0, 1, 2, ..., 9]
rg = Array[ "one", "two", "three" ] || [ "foo", "bar" ]
rg[-1] // access last element in array, or rg.first / rg.last
rg.index("two") == 1 // lookup index of item
rg1 & rg2 // intersect of arrays (only common elements)
rg1 - rg2 // difference (only unique elements)
rg1 | rg2 // union (join with dupes removed)
rg.pop || rg.push || rg.shift || rg.unshift // stack operations
Array.clear
Array.empty? // true | false
Hash / Dictionary
Hash.new || Hash[ :key1, "Value1", ... ] || Hash[ :key1 => "Value1", ... ]
Hash.new("month") // hash with a default value - the one returned if key has no value associated with it
h = {symbol: "value"} // 1.9 using symbol as hash key
h = {:symbol => "value"} // <1.9 ruby using symbol as hash key
h.has_key? :key1 || h.has_value? "Value1" || h[:key]
h.keys // list keys
h.values // list values
h.delete( :key )
h.delete_if { |k,v| v == "Value1" }
h.clear || h.empty?
h.each { |k,v| puts "#{k} / #{v}" } // loop through each key-value pair
h.each_key || h.each_value // just keys or values
Classes:
class Hello < Greeting // Hello extends (inherits) Greeting
@@size = 0 // class variable
attr :onlyget
attr :getandset, true // second argument true
attr_reader :gone, :here // getter
attr_writer :count, :set // setters
attr_accessor :start, :stop // accessors
def initialize( arg1 ) // c'tor
@val = arg1 // @ == instance variable
end
class << self // singleton class, instantiated by the enclosing class
def polygon(vertices, length)
-- snip --
end
end
def Hello.bye // Class method
puts "Goodbye"
end
private // methods below here are private (also can use protected)
def hidden
... snip ...
end
end
Hello.polygon(2, 5)
Hello.instance_methods - Object.instance_methods // print out the Hello specific methods
h = Hello.new( "Test" )
h.respond_to? (:gone) // test if instance responds to method invocation
Blocks:
Nameless functions (effectively a closure). Can be wrapped in 'do' 'end' or or braces {}. Braces have higher precedence.
['purple', 'monkey', 'dishwasher'].each { |e| puts e }
or
['purple', 'monkey', 'dishwasher'].each do |element| puts element end
Automatically convert block to proc, prefix param with & (ampersand)
def return_proc( &proc )
yield
end
return_proc { puts "Convert block to proc" }
Procs / Lambda:
Store procedures as objects complete with context. Invoke with call method (count.call)
count = Proc.new { [1,2,3,4,5].each do |i| print i end; puts }
your_proc = lambda { puts "Lurch: 'You rang?'" }
my_proc = proc { puts "Morticia: 'Who was at the door, Lurch?'" }
Note: lambda / proc is preferred to Proc.new.
Modules:
like namespaces, a Module/class including a module inherits it's contents.
Must be named as a constant (capital letter).
include Mymodule // if in same file
require 'Mymodule' // if module is in a separate file
Can define module methods by prefixing method with module name (e.g. def Mymodule.method)
Exception handling:
rescue analogous to catch, ensure analogous to finally in Java.
begin
// do stuff
rescue ZeroDivisionError // type of exception
// do stuff
ensure
// do stuff
end
// throw / catch
def test(val)
throw ( :zero ) if val <= 0
return 5 / val
end
catch( :zero ) { test(-11) }
Metaprogramming:
write a program (or part of) using another program. 'define_method' in Module is key element - creates methods on the fly.
class Foo
%w{ foo bar yar }.each do |n|
define_method(n) { puts "method #{n}" }
end
end
Foo.new.bar // prints 'method bar'
Miscellaneous:
- alias - reference to another method. A way to have access to overridden methods. (alias <new-name> <existing-method>)
- yield - Used within a method to execute a block associated with it. Can test for presence with block_given? test (def doit if block_given? yield else puts "no block" end end)
- BEGIN / END can define blocks that execute before and after a program runs (BEGIN { puts "Date and time: " + Time.now.to_s } )
- .class method returns type of object being called
- irb - command line ruby interpreter
- ri - command line ruby documentation, i.e. 'ri Array'
