Module: Erlang::Associable

Included in:
Map, Tuple
Defined in:
lib/erlang/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 Tuple#fetch, Tuple#put, Map#fetch, and Map#put for examples.

Licensing

Portions taken and modified from https://github.com/hamstergem/hamster

Copyright (c) 2009-2014 Simon Harris

Permission is hereby granted, free of charge, to any person obtaining
a copy of this software and associated documentation files (the
"Software"), to deal in the Software without restriction, including
without limitation the rights to use, copy, modify, merge, publish,
distribute, sublicense, and/or sell copies of the Software, and to
permit persons to whom the Software is furnished to do so, subject to
the following conditions:

The above copyright notice and this permission notice shall be
included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

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 Erlang type doesn't understand, raises an argument error

Examples:

m = Erlang::Map[:a => 9, :b => Erlang::Tuple['a', 'b'], :e => nil]
m.dig(:b, 0)    # => "a"
m.dig(:b, 5)    # => nil
m.dig(:b, 0, 0) # => nil
m.dig(:b, :a)   # ArgumentError

Parameters:

  • key —

    to fetch from the collection

Returns:

  • (Object) 


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# File 'lib/erlang/associable.rb', line 89

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

t = Erlang::Tuple[123, 456, 789, Erlang::Map["a" => Erlang::Tuple[5, 6, 7]]]
t.update_in(3, "a", 1) { |value| value + 9 }
# => Erlang::Tuple[123, 456, 789, Erlang::Map["a'" => Erlang::Tuple[5, 15, 7]]]
map = Erlang::Map["a" => Erlang::Map["b" => Erlang::Map["c" => 42]]]
map.update_in("a", "b", "c") { |value| value + 5 }
# => Erlang::Map["a" => Erlang::Map["b" => Erlang::Map["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/erlang/associable.rb', line 63

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, EmptyMap)
    new_value = value.update_in(*key_path[1..-1], &block)
  end
  return put(key, new_value)
end