Confusion with `Array#each` in Ruby

Question

Confusion with Array#each as below:

%w{ david black }.each {|str| str.capitalize }
#=> ["david", "black"]

The above code is cool,but how the below logic works,couldn't understand.

%w{ david black }.each(&:capitalize)
#=> ["david", "black"]

Answer 1

It's a very old trick, called Symbol#to_proc .

You can read more about it here: http://pragdave.pragprog.com/pragdave/2005/11/symbolto_proc.html

Basically, it's a shortcut for calling methods that take no args. Often used in map , for example.

%w[i can measure length of strings].map(&:length) # => [1, 3, 7, 6, 2, 7]

Answer 2

How about using map?

[1173]pry(main)> ["david","black"].map{|str| str.capitalize }
=> ["David","Black"]
[1173]pry(main)>

Answer 3

The notation of &:something does for every element of the array the method something .

This is usually used with map to change every entry of the array or to extract data from hashes.

[{:foo => :bar, :meh => :bar2}, {:foo => :one, :meh => :two}].map(&:foo)
=> [:bar, :one]

Answer 4

I don't get your example with .each, maybe you meant .map

When you pass in the &:method_name it's shorthand for doing it in the block. So for each item apply this method.