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require "naught/null_class_builder/command"
module Naught
class NullClassBuilder
module Commands
# Enables null-safe proxy wrapping via the NullSafe() conversion function
#
# When enabled, the generated null class gains a NullSafe() function that
# wraps any value in a proxy. The proxy intercepts all method calls and
# wraps return values, replacing nil with the null object.
#
# @example Enable null-safe proxy
# NullObject = Naught.build do |config|
# config.null_safe_proxy
# end
#
# include NullObject::Conversions
#
# user = nil
# NullSafe(user).name.upcase # => <null>
#
# user = OpenStruct.new(name: nil)
# NullSafe(user).name.upcase # => <null>
#
# user = OpenStruct.new(name: "Bob")
# NullSafe(user).name.upcase # => "BOB"
#
# @api private
class NullSafeProxy < Command
# Install the NullSafe conversion function
# @return [void]
# @api private
def call
null_equivs = builder.null_equivalents
defer_class do |null_class|
proxy_class = build_proxy_class(null_class, null_equivs)
null_class.const_set(:NullSafeProxy, proxy_class)
install_null_safe_conversion(null_class, proxy_class, null_equivs)
end
end
private
# Build the proxy class that wraps objects for null-safe access
#
# @param null_class [Class] the null object class
# @param null_equivs [Array<Object>] values treated as null-equivalent
# @return [Class] the proxy class
# @api private
def build_proxy_class(null_class, null_equivs)
Class.new(::Naught::BasicObject) do
include ::Naught::NullSafeProxyTag
define_method(:initialize) { |target| @target = target }
define_method(:__target__) { @target }
define_method(:respond_to?) { |method_name, include_private = false| @target.respond_to?(method_name, include_private) }
define_method(:inspect) { "<null-safe-proxy(#{@target.inspect})>" }
define_method(:method_missing) do |method_name, *args, &block|
result = @target.__send__(method_name, *args, &block)
case result
when ::Naught::NullObjectTag then result
when *null_equivs then null_class.get
else self.class.new(result)
end
end
klass = self
define_method(:class) { klass }
end
end
# Install the NullSafe conversion method on the Conversions module
#
# @param null_class [Class] the null object class
# @param proxy_class [Class] the proxy class
# @param null_equivs [Array<Object>] values treated as null-equivalent
# @return [void]
# @api private
def install_null_safe_conversion(null_class, proxy_class, null_equivs)
null_class.const_get(:Conversions).define_method(:NullSafe) do |object|
case object
when ::Naught::NullObjectTag then object
when *null_equivs then null_class.get
else proxy_class.new(object)
end
end
end
end
end
end
end
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