Issue #15301 has been updated by marcandre (Marc-Andre Lafortune).


shevegen (Robert A. Heiler) wrote:
>     [[1, -2], [-3, -4]].map(&:map.(&:abs)) # => [[1, 2], [3, 4]]
> 
> I think using .map twice like that is a bit odd. Matz likes DRI

You probably misunderstood what the example is doing. `map` is not repeated per say here. You can replace the first one by `flat_map` for example:

```
[[1, -2], [-3, -4]].flat_map(&:map.(&:abs)) # => [1, 2, 3, 4]
```


----------------------------------------
Feature #15301: Symbol#call, returning method bound with arguments
https://bugs.ruby-lang.org/issues/15301#change-74856

* Author: zverok (Victor Shepelev)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
----------------------------------------
In one Reddit discussion I've got stuck with this simple, yet seemingly powerful idea, not sure if it was discussed anytime previously (can't find on the bug tracker, but maybe I am just bad at searching):

```ruby
class Symbol
  def call(*args, &block)
    proc { |x| x.send(self, *args, &block) }
  end
end

[10, 20, 30].map &:modulo.(3) # => [1, 2, 0]
[[1, -2], [-3, -4]].map(&:map.(&:abs)) # => [[1, 2], [3, 4]]
[1, 2, 3, 4].map &:**.(2) # => [1, 4, 9, 16]
```

I understand and respect core team's reluctance for adding new methods to core classes, but from the top of my head I can't invent _incredibly_ bad consequences (there, of course, could be some codebases that defined their own `Symbol#call` in a different way, but I don't estimate the probability as super-high; and the same could be said almost for any new method).

On the other hand, resulting code seems pretty nice, "Rubyish", explainable and mostly unambiguous. 

Would like to hear other's opinions.

PS: One obvious objection could be that it is almost a de-facto standard to have any object's `#to_proc` to return proc doing exactly the same what the `#call` does (if the object happen to have both). It is unfortunate, but I believe the people will use to it, considering the possible gains. And, anyway, that's only "de-facto" rule, not the language standard :) 



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