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module Virtus
# Define equality, equivalence and inspection methods
class Equalizer < Module
# Initialize an Equalizer with the given keys
#
# Will use the keys with which it is initialized to define #cmp?,
# #hash, and #inspect
#
# @param [String] name
#
# @param [Array<Symbol>] keys
#
# @return [undefined]
#
# @api private
def initialize(name, keys = [])
@name = name.dup.freeze
@keys = keys.dup
define_methods
include_comparison_methods
end
# Append a key and compile the equality methods
#
# @return [Equalizer] self
#
# @api private
def <<(key)
@keys << key
self
end
private
# Define the equalizer methods based on #keys
#
# @return [undefined]
#
# @api private
def define_methods
define_cmp_method
define_hash_method
define_inspect_method
end
# Define an #cmp? method based on the instance's values identified by #keys
#
# @return [undefined]
#
# @api private
def define_cmp_method
keys = @keys
define_method(:cmp?) do |comparator, other|
keys.all? { |key| send(key).send(comparator, other.send(key)) }
end
end
# Define a #hash method based on the instance's values identified by #keys
#
# @return [undefined]
#
# @api private
def define_hash_method
keys = @keys
define_method(:hash) do
keys.map { |key| send(key) }.push(self.class).hash
end
end
# Define an inspect method that reports the values of the instance's keys
#
# @return [undefined]
#
# @api private
def define_inspect_method
name, keys = @name, @keys
define_method(:inspect) do
"#<#{name}#{keys.map { |key| " #{key}=#{send(key).inspect}" }.join}>"
end
end
# Include the #eql? and #== methods
#
# @return [undefined]
#
# @api private
def include_comparison_methods
module_eval { include Methods }
end
# The comparison methods
module Methods
# Compare the object with other object for equality
#
# @example
# object.eql?(other) # => true or false
#
# @param [Object] other
# the other object to compare with
#
# @return [Boolean]
#
# @api public
def eql?(other)
instance_of?(other.class) && cmp?(__method__, other)
end
# Compare the object with other object for equivalency
#
# @example
# object == other # => true or false
#
# @param [Object] other
# the other object to compare with
#
# @return [Boolean]
#
# @api public
def ==(other)
other.kind_of?(self.class) && cmp?(__method__, other)
end
end # module Methods
end # class Equalizer
end # module Virtus
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