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Feature #17330

Updated by nobu (Nobuyoshi Nakada) about 1 year ago

(As always "with core" method proposals, I don't expect quick success, but hope for a fruitful discussion) 

 ### Reasons: 

 Ruby always tried to be very chainability-friendly. Recently, with introduction of `.then` and `=>`, even more so. But one pattern that frequently emerges and doesn't have good idiomatic expression: calculate something, and if it is not a "good" value, return `nil` (or provide default value with `||`). There are currently two partial solutions: 

 1. `nonzero?` in Ruby core (frequently mocked for "inadequate" behavior, as it is looking like predicate method, but instead of `true`/`false` returns an original value or `nil`) 
 2. ActiveSupport `Object#presence`, which also returns an original value or `nil` if it is not "present" (e.g. `nil` or `empty?` in AS-speak) 

 Both of them prove themselves quite useful in some domains, but they are targeting only those particular domains, look unlike each other, and can be confusing. 

 ### Proposal: 

 Method `Object#non` (or `Kernel#non`), which receives a block, calls it with receiver and returns `nil` (if block matched) or receiver otherwise. 

 ##### Prototype implementation: 

 ```ruby 
 class Object 
   def non 
     self unless yield(self) 
   end 
 end 
 ``` 

 ##### Usage examples: 

 1. With number: 

     ```ruby 
     limit = calculate.some.limit 
     limit.zero? ? DEFAULT_LIMIT : limit 
     # or, with nonzero? 
     calculate.some.limit.nonzero? || DEFAULT_LIMIT 
     # with non: 
     calculate.some.limit.non(&:zero?) || DEFAULT_LIMIT 
     # ^ Note here, how, unlike `nonzero?`, we see predicate-y ?, but it is INSIDE the `non()` and less confusing 
     ``` 

 2. With string: 

     ```ruby 
     name = params[:name] if params[:name] && !params[:name].empty? 
     # or, with ActiveSupport: 
     name = params[:name].presence 
     # with non: 
     name = params[:name]&.non(&:empty?) 
     ``` 

 3. More complicated example 

     ```ruby 
     action = payload.dig('action', 'type') 
     return if PROHIBITED_ACTIONS.include?(action) 
     send("do_#{action}") 
     # with non & then: 
     payload.dig('action', 'type') 
       .non { |action| PROHIBITED_ACTIONS.include?(action) } 
       &.then { |action| send("do_#{action}") } 
     ``` 

 ### Possible extensions of the idea 

 It is quite tempting to define the symmetric method named -- as we already have `Object#then` -- `Object#when`: 
 ```ruby 
 some.long.calculation.when { |val| val < 10 } # returns nil if value >= 10 
 # or even... with support for === 
 some.long.calculation.when(..10)&.then { continue to do something } 
 ``` 
 ...but I am afraid I've overstayed my welcome :) 

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