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ruby enumerable & to_proc (ampersond & symbol shortcut)

by sandipransing 0 comments

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"]

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