class Value
`Value` generates `Struct` classes with safer constructors. It is designed to provide a superset of the interface of the `Values` gem, with better performance, by subclassing actual native Structs.
`Value` constructors require all mandatory arguments to be provided, and supply default values for all optional arguments. Additionally, the resulting instance is frozen. To obtain a mutable Value
, `dup` the result.
`Value` structure classes are created similarly to `Struct`s, with the addition that optional arguments are may be specified as keyword arguments: `ValueType = Value.new
(:a, :b, c: default_value)`. The default values to optional arguments are saved at class creation time and supplied as default constructor arguments to instances. Default values are aliased, so providing mutable defaults is discouraged.
Two instance constructors are provided, with positional and keyword arguments.
Value
types may be constructed with positional arguments using `new`. Arguments are provided in the same order as specified at class initialization time, with mandatory arguments before optional ones. For example: `ValueType.new(1, 2)`, `ValueType.new(1, 2, 3)`
Value
types may be constructed with keyword arguments using `with`. For example: `ValueType.with(a: 1, b: 2, c: 3)`
Public Class Methods
# File lib/value.rb, line 29 def new(*required_args, **optional_args, &block) arguments = {} required_args.each { |arg| arguments[arg] = true } optional_args.each_key { |arg| arguments[arg] = false } validate_names(*arguments.keys) clazz = super(*arguments.keys, &nil) # define class and instance methods in modules so that the class can # override them keyword_constructor = generate_keyword_constructor(arguments) class_method_module = Module.new do module_eval(keyword_constructor) define_method(:__constructor_default) do |name| optional_args.fetch(name) end end clazz.extend(class_method_module) constructor = generate_constructor(arguments) instance_method_module = Module.new do module_eval(constructor) end clazz.include(instance_method_module) # Evaluate the block in the context of the class clazz.class_eval(&block) if block_given? clazz end
Private Class Methods
Generates an initialize method with required and optional parameters, delegating to the Struct constructor. Parameter names must have already been validated.
For a Value.new
(:a, b: x), will define the method:
def initialize(a, b = self.class.__constructor_default(:b))
super(a, b) freeze
end
# File lib/value.rb, line 80 def generate_constructor(arguments) params = arguments.map do |arg_name, required| if required arg_name else "#{arg_name} = self.class.__constructor_default(:#{arg_name})" end end <<-SRC def initialize(#{params.join(", ")}) super(#{arguments.keys.join(", ")}) freeze end SRC end
Generates an alternative construction method accepting keyword arguments for required and optional parameters, delegating to the generated constructor. Parameter names must have already been validated.
For a Value.new
(:a, b: x), will define the (class) method:
def with(a:, b: __constructor_default(:b))
self.new(a, b)
end
# File lib/value.rb, line 106 def generate_keyword_constructor(arguments) params = arguments.map do |arg_name, required| if required "#{arg_name}:" else "#{arg_name}: __constructor_default(:#{arg_name})" end end <<-SRC def with(#{params.join(", ")}) self.new(#{arguments.keys.join(", ")}) end SRC end
# File lib/value.rb, line 62 def validate_names(*params) params.each do |param| unless param.is_a?(Symbol) && param =~ /\A[a-z_][a-zA-Z_0-9]*\z/ raise ArgumentError.new("param #{param} is not a valid identifier") end end end
Public Instance Methods
# File lib/value.rb, line 123 def with(**kwargs) return self if kwargs.empty? self.class.with(**to_h.merge(kwargs)) end