what ruby tap method does on a {} [duplicate]

Question

I've read about what tap does in Ruby but I'm confused by the code block below,

{}.tap do |h|
  # some hash processing
end

any help would be greatly appreciated.

Answer 1

#tap method simply passes an object it was called on to a block. At the end of the block it returns the same object again. This way you can chain operations or restrict variable scope.

{}.tap { |h| h[:a] = 1 }.size # => 1

You were able to chain a next method to this block. And also avoided creating a h variable in your scope.

Answer 2

tap is particularyl useful if you want to do some modifications on the hash and after that return it, e.g. inside a method that returns the hash. The advantage of tap being that you don't have to explitely return the hash at the end and there's no need for an intermediary variable.

hash = {}
hash[:a] = 'b'
hash
# => {:a=>"b"}

vs.

{}.tap do |hash|
  hash[:a] = 'b'
end
# => {:a=>"b"}