lib/hamster/associable.rb
module Hamster
# 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.
module 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.
#
# @example
# 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]]]
#
# @param key_path [Object(s)] List of keys/indexes which form the path to the key to be modified
# @yield [value] The previously stored value
# @yieldreturn [Object] The new value to store
# @return [Associable]
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
# 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
#
# @example
# 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
# @params keys to fetch from the collection
# @return [Object]
def dig(key, *rest)
value = get(key)
if rest.empty? || value.nil?
value
elsif value.respond_to?(:dig)
value.dig(*rest)
end
end
end
end