Issue #20326 has been updated by mame (Yusuke Endoh). Personally, I don't like an API that distinguishes between "nil is passed" and "nothing is passed". I don't think we should introduce any feature to encourage such an API. When we want to conditionally pass the argument to such an API, we need to write `optional_val ? api(optional_val) : api()` or `args = [optional_val].compact; api(*args)` or something ugly. Instead, I hope such an API just accepts and ignores `nil`. It would be good enough in most cases. ---------------------------------------- Feature #20326: Add an `undefined` for use as a default argument. https://bugs.ruby-lang.org/issues/20326#change-107147 * Author: shan (Shannon Skipper) * Status: Feedback ---------------------------------------- Variations around `UNDEFINED = Object.new` are a fairly common pattern to see used as default arguments to distinguish between `nil` and no argument provided. For example, a Ruby implementation of Array#count might look something like: ``` ruby class Array UNDEFINED = Object.new def UNDEFINED.inspect = 'UNDEFINED' UNDEFINED.freeze def count(item = UNDEFINED) if item == UNDEFINED # ... end end end ``` I'd like to propose adding an `undefined` module function method on Kernel to remove the boilerplate for this fairly common use case. An `__undefined__` method or `__UNDEFINED__` keyword would be alternatives to `undefined`. An `undefined?` helper would also be an optional nicety: ``` ruby class Array def count(item = undefined) if item.undefined? # ... end end end ``` A Ruby implementation might look like: ``` ruby module Kernel UNDEFINED = Object.new def UNDEFINED.inspect = -'undefined' UNDEFINED.freeze private_constant :UNDEFINED def undefined? = self == UNDEFINED module_function def undefined = UNDEFINED end ``` -- https://bugs.ruby-lang.org/