Basically Enumerable mixin gives collection classes a variety of traverse, search, sort methods.
understanding ruby blocks i.e. proc
blocks are statements of code written in ruby. one can take them as similar to c language macro's
Different ways to define blocks
a = proc do puts "hello" end a.call #=> hello b = lambda do |u| puts "hello #{u}" end b.call('sandip')#=> hello sandip c = proc {|user| puts user } c.call('sandip') #=> sandip Passing block to enumerator
Lets assume we have collection array of strings and we want to print it
a = ['hi', 'sandip', 'how', 'you', 'doing', '?'] => ["hi", "sandip", "how", "you", "doing", "?"] a.each {|w| puts w } q = proc {|w| puts w } => # a.each(&q) #=> hi sandip how you doing ? a.map{|r| q.call(r)} #=> hi sandip how you doing ? Understanding symbol#to_proc
Symbol has method to_proc which converts symbol to block where symbol is taken as method to be executed on first argument of proc
How to_proc got implemented inside Symbol class class Symbol def to_proc Proc.new { |*args| args.shift.__send__(self, *args) } end end Lets have some examples
v = :even?.to_proc # equivalent to proc {|a| a.even?} #=> # q = [1, 2, 3, 5, 67] q.map(&v) => [false, true, false, false, false] Is there any shortcut?
Yes, there is shortcut to have block passed to enumerators on the fly using ampersand followed by colon (i.e. symbol)
q = [1, 2, 3, 5, 67] q.map(&:even?) <=> q.map(&:even?.to_proc) q.map(&:even?.to_proc) #=> [false, true, false, false, false] q.map(&:even?) #=> [false, true, false, false, false] Some handy examples
[1, 2, 3, 5, 67].inject(&:+) #=> 78 [1, 2, 3, 5, 67].inject(:+) #=> 78 [1, 2, 3, 5, 67].any?(&:even?) #=> true [1, 2, 3, 5, 67].detect(&:even?) #=> 2 ['ruby', 'on', 'rails'].map(&:upcase) #=> ["RUBY", "ON", "RAILS"]