Hash#merge

Returns the new Hash formed by merging each of other_hashes into a copy of self.

Each argument in other_hashes must be a Hash.

With arguments and no block:

• Returns the new Hash object formed by merging each successive Hash in other_hashes into self.

• Each new-key entry is added at the end.

• Each duplicate-key entry’s value overwrites the previous value.

Example:

h = {foo: 0, bar: 1, baz: 2}
h1 = {bat: 3, bar: 4}
h2 = {bam: 5, bat:6}
h.merge(h1, h2) # => {:foo=>0, :bar=>4, :baz=>2, :bat=>6, :bam=>5}

With arguments and a block:

• Returns a new Hash object that is the merge of self and each given hash.

• The given hashes are merged left to right.

• Each new-key entry is added at the end.

• For each duplicate key:

  • Calls the block with the key and the old and new values.

  • The block’s return value becomes the new value for the entry.

Example:

h = {foo: 0, bar: 1, baz: 2}
h1 = {bat: 3, bar: 4}
h2 = {bam: 5, bat:6}
h3 = h.merge(h1, h2) { |key, old_value, new_value| old_value + new_value }
h3 # => {:foo=>0, :bar=>5, :baz=>2, :bat=>9, :bam=>5}

With no arguments:

• Returns a copy of self.

• The block, if given, is ignored.

Example:

h = {foo: 0, bar: 1, baz: 2}
h.merge # => {:foo=>0, :bar=>1, :baz=>2}
h1 = h.merge { |key, old_value, new_value| raise 'Cannot happen' }
h1 # => {:foo=>0, :bar=>1, :baz=>2}