Exciting! It was apparently put up yesterday, on Christmas. What a cool gift right? I looked through the changed maintained my Mauricio and here are /my/ favorites.

New literal hash syntax [Ruby2]

{a: "foo"}    # => {:a=>"foo"}

.() and calling Procs without #call/#[] [EXPERIMENTAL]

You can now do:

a = lambda{|*b| b} a.(1,2) # => [1, 2]

Multiple splats allowed

1.9 allows multiple splat operators when calling a method:

def foo(*a)
     a
   end

   foo(1, *[2,3], 4, *[5,6])                        # => [1, 2, 3, 4, 5, 6]

Mandatory arguments after optional arguments allowed

def m(a, b=nil, *c, d)
     [a,b,c,d]
   end
   m(1,2)                                         # => [1, nil, [], 2]

Object#tap

Passes the object to the block and returns it (meant to be used for call chaining).

"F".tap{|x| x.upcase!}[0] # => "F" # Note that "F".upcase![0] would fail since upcase! would return nil in this # case.

Module#attr is an alias of attr_reader

Use

attr :foo=

to create a read/write accessor. (RCR#331)

Enumerable#cycle

Calls the given block for each element of the enumerable in a never-ending cycle:

a = ["a", "b", "c"]
a.cycle {|x| puts x }  # print, a, b, c, a, b, c,.. forever.

Enumerable#group_by

Groups the values in the enumerable according to the value returned by the block:

(1..10).group_by{|x| x % 3} # => {0=>[3, 6, 9], 1=>[1, 4, 7, 10], 2=>[2, 5, 8]}

Enumerable#drop

Without a block, returns an array with all but the first n elements from the enumeration. Otherwise drops elements while the block returns true (and returns all the elements after it returns a false value):

a = [1, 2, 3, 4, 5] a.drop(3) # => [4, 5]
a.drop {|i| i < 3 } # => [3, 4, 5]

Enumerable#inject (#reduce) without a block

If no block is given, the first argument to #inject is the name of a two-argument method that will be called; the optional second argument is the initial value:

[RUBY_VERSION, RUBY_RELEASE_DATE] # => ["1.9.0", "2007-08-03"] (1..10).reduce(:+) # => 55

Enumerable#count

It could be defined in Ruby as

def count(*a) inject(0) do |c, e| if a.size == 1 # suspect, but this is how it works (a[0] == e) ? c + 1 : c else yield(e) ? c + 1 : c end end end

Therefore

["bar", 1, "foo", 2].count(1) # => 1 ["bar", 1, "foo", 2].count{|x| x.to_i != 0} # => 2

Array#nitems

It is equivalent to selecting the elements that satisfy a condition and obtaining the size of the resulting array:

%w[1 2 3 4 5 6].nitems{|x| x.to_i > 3}    # => 3

Block argument to Array#index, Array#rindex [Ruby2]

They can now take a block to make them work like #select.

['a','b','c'].index{|e| e == 'b'} # => 1 ['a','b','c'].index{|e| e == 'c'} # => 2 ['a','a','a'].rindex{|e| e == 'a'} # => 2 ['a','a','a'].index{|e| e == 'b'} # => nil

Array#combination

ary.combination(n){|c| ...}

yields all the combinations of length n of the elements in the array to the given block. If no block is passed, it returns an enumerator instead. The order of the combinations is unspecified.

a = [1, 2, 3, 4] a.combination(1).to_a #=> [[1],[2],[3],[4]] a.combination(2).to_a #=> [[1,2],[1,3],[1,4],[2,3],[2,4],[3,4]] a.combination(3).to_a #=> [[1,2,3],[1,2,4],[1,3,4],[2,3,4]] a.combination(4).to_a #=> [[1,2,3,4]] a.combination(0).to_a #=> [[]]: one combination of length 0 a.combination(5).to_a #=> [] : no combinations of length 5

Array#permutation

Operates like #combination, but with permutations of length n.
<code lang="ruby">a = [1, 2, 3] a.permutation(1).to_a #=> [[1],[2],[3]] a.permutation(2).to_a #=> [[1,2],[1,3],[2,1],[2,3],[3,1],[3,2]] a.permutation(3).to_a #=> [[1,2,3],[1,3,2],[2,1,3],[2,3,1],[3,1,2],[3,2,1]] a.permutation(0).to_a #=> [[]]: one permutation of length 0 a.permutation(4).to_a #=> [] : no permutations of length 4

Array#pop, Array#shift

They can take an argument to specify how many objects to return:

%w[a b c d].pop(2) # => ["c", "d"]

Hash preserves order!

RUBY_VERSION                    # => "1.9.0"
h={:a=>1, :b=>2, :c=>3, :d=>4}  # => {:a=>1, :b=>2, :c=>3, :d=>4}
h[:e]=5
h                                           # => {:a=>1, :b=>2, :c=>3, :d=>4, :e=>5}

h.keys                                      # => [:a, :b, :c, :d, :e]
h.values                                    # => [1, 2, 3, 4, 5]
h.to_a                                      # => [[:a, 1], [:b, 2], [:c, 3], [:d, 4], [:e, 5]]

vs.

RUBY_VERSION                    # => "1.8.6"
h={:a=>1, :b=>2, :c=>3, :d=>4}  # => {:a=>1, :b=>2, :c=>3, :d=>4}
h[:e]=5
h                                           # => {:e=>5, :a=>1, :b=>2, :c=>3, :d=>4}
h.keys                                      # => [:e, :a, :b, :c, :d]
h.values                                    # => [5, 1, 2, 3, 4]
h.to_a                                      # => [[:e, 5], [:a, 1], [:b, 2], [:c, 3], [:d, 4]]

Numeric#upto, #downto, #times, #step

These methods return an enumerator if no block is given:

a = 10.times a.inject{|s,x| s+x } # => 45 a = [] b = 10.downto(5) b.each{|x| a << x} a # => [10, 9, 8, 7, 6, 5]

Range#cover?

range.cover?(value)

compares value to the begin and end values of the range, returning true if it is comprised between them, honoring #exclude_end?.

("a".."z").cover?("c")                            # => true
("a".."z").cover?("5")                            # => false

Limit input in IO#gets, IO#readline, IO#readlines, IO#each_line, IO#lines, IO.foreach, IO.readlines, StringIO#gets, StringIO#readline, StringIO#each, StringIO#readlines

These methods accept an optional integer argument to specify the maximum amount of data to be read. The limit is specified either as the (optional) second argument, or by passing a single integer argument (i.e. the first argument is interpreted as the limit if it’s an integer, as a line separator otherwise).

IO#ungetc, StringIO#ungetc

Allows to push back an arbitrarily large character.

Seven predicate methods where added for the weekdays:

Time.now        # => Thu Nov 03 18:58:25 CET 2005
Time.now.sunday?        # => false