Feature #17330
Updated by zverok (Victor Shepelev) over 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}") }
```
Basically, ### Possible extensions of the proposal idea
It is a "chainable guard clause" that allows quite tempting to "chain"ify and DRYify code like:
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 = fetch_something >= 10
return value unless value.with_problems?
# which turns into
fetch_something.non(&:with_problems?)
# or even... with support for ===
value = fetch_something some.long.calculation.when(..10)&.then { continue to do something }
value = reasonable_default if value.with_problems? ```
# turns into ...but I am afraid I've overstayed my welcome :)
value = fetch_something.non(&:with_problems?) || reasonable_default
```
I believe that this idiom is frequent enough, in combinations like (assorted examples) "read config file but return `nil` if it is empty/wrong version", "fetch latest invoice, but ignore if it has an `unpayable` flag", "fetch a list of last user's searches, but if it is empty, provide default search hints" etc.
I believe there _is_ un unreflected need for idiom like this, the need that is demonstrated by the existence of `nonzero?` and `presence`.