Module: Hamster::Associable

Included in:
Hash, Vector
Defined in:
lib/hamster/associable.rb

Overview

Including `Associable` in your container class gives it an `update_in` method.

To mix in `Associable`, your class must implement two methods:

  • `fetch(index, default = (missing_default = true))`

  • `put(index, item = yield(get(index)))`

  • `get(key)`

See Vector#fetch, Vector#put, Hash#fetch, and Hash#put for examples.

Instance Method Summary collapse

Instance Method Details

#dig(key, *rest) ⇒ Object

Return the value of successively indexing into a collection. If any of the keys is not present in the collection, return `nil`. keys that the Hamster type doesn't understand, raises an argument error

Examples:

h = Hamster::Hash[:a => 9, :b => Hamster::Vector['a', 'b'], :e => nil]
h.dig(:b, 0)    # => "a"
h.dig(:b, 5)    # => nil
h.dig(:b, 0, 0) # => nil
h.dig(:b, :a)   # ArgumentError

Returns:

  • (Object)

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# File 'lib/hamster/associable.rb', line 62

def dig(key, *rest)
  value = get(key)
  if rest.empty? || value.nil?
    value
  elsif value.respond_to?(:dig)
    value.dig(*rest)
  end
end

#update_in(*key_path) {|value| ... } ⇒ Associable

Return a new container with a deeply nested value modified to the result of the given code block. When traversing the nested containers non-existing keys are created with empty `Hash` values.

The code block receives the existing value of the deeply nested key/index (or `nil` if it doesn't exist). This is useful for “transforming” the value associated with a certain key/index.

Naturally, the original container and sub-containers are left unmodified; new data structure copies are created along the path as needed.

Examples:

v = Hamster::Vector[123, 456, 789, Hamster::Hash["a" => Hamster::Vector[5, 6, 7]]]
v.update_in(3, "a", 1) { |value| value + 9 }
# => Hamster::Vector[123, 456, 789, Hamster::Hash["a" => Hamster::Vector[5, 15, 7]]]
hash = Hamster::Hash["a" => Hamster::Hash["b" => Hamster::Hash["c" => 42]]]
hash.update_in("a", "b", "c") { |value| value + 5 }
# => Hamster::Hash["a" => Hamster::Hash["b" => Hamster::Hash["c" => 47]]]

Parameters:

  • key_path (Object(s))

    List of keys/indexes which form the path to the key to be modified

Yields:

  • (value)

    The previously stored value

Yield Returns:

  • (Object)

    The new value to store

Returns:


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# File 'lib/hamster/associable.rb', line 36

def update_in(*key_path, &block)
  if key_path.empty?
    raise ArgumentError, "must have at least one key in path"
  end
  key = key_path[0]
  if key_path.size == 1
    new_value = block.call(fetch(key, nil))
  else
    value = fetch(key, EmptyHash)
    new_value = value.update_in(*key_path[1..-1], &block)
  end
  put(key, new_value)
end