Deep Merge: transliterated from https://gist.github.com/dpatti/178bd9948518256396ff

deep-merge.rb

# Deep merge
# 
# - Write a function that takes two hashes and returns a new hash containing the
#   keys and values from both hashes.
# - Neither input should be modified.
# - If the key exists in both hashes...
#   ...merge the values if they are both hashes.
#   ...give the values in the second hash (b) precedence otherwise.

def merge(a, b)
  # replace with your solution
end

# Input for tests
a = {
  "hello" => "who?",
  "foo" => {
    "bar" => 1,
  },
  "first" => true,
}

b = {
  "hello" => "world!",
  "foo" => {
    "baz" => 2,
  },
  "second" => false,
}

expected = {
  "hello" => "world!",
  "foo" => {
    "bar" => 1,
    "baz" => 2,
  },
  "first" => true,
  "second" => false,
}

# Test that the merge gives us the expected results
result = merge(a, b)
unless result == expected
  puts 'expected:', expected.inspect, 'result:', result.inspect
  raise RuntimeError, 'unexpected results'
end

# Test that we have not modified the input
raise RuntimeError, 'the first input was modified' unless a == {
  "hello" => "who?",
  "foo" => {
    "bar" => 1,
  },
  "first" => true,
}

raise RuntimeError, 'the second input was modified' unless b == {
  "hello" => "world!",
  "foo" => {
    "baz" => 2,
  },
  "second" => false,
}

puts "All tests pass!"