Issue #12115 has been updated by duerst (Martin Drst).


nobu (Nobuyoshi Nakada) wrote:
> jwmittag (Jrg W Mittag) wrote:
> > I disagree: responding to `to_proc` in Ruby more or less means "I am a function-like thing". And arrays *are* function-like things, they are basically functions from their indices to their values. Having `to_proc` mean something *different* than that would be a big mistake, IMO. It would also be inconsistent with `Hash#to_proc`.
> 
> Even if arrays were function-like things, the elements are not arguments.

In Jrg's proposals, array elements are indeed not arguments, they are return values. Index values are arguments.

----------------------------------------
Feature #12115: Add Symbol#call to allow to_proc shorthand with arguments
https://bugs.ruby-lang.org/issues/12115#change-67086

* Author: felixbuenemann (Felix Bnemann)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
----------------------------------------
I am a great fan of the `Symbol#to_proc` shorthand when mapping or reducing collections:

```ruby
[1,2,16].map(&:to_s)
=> ["1", "2", "16"]
[1,2,16].reduce(&:*)
=> 32
```

I often wish it would be possible to pass an argument to the method when doing this, which currently requires a block and is more verbose:

```ruby
[1,2,16].map { |n| n.to_s(16) }
=> ["1", "2", "10"]
# active_support example
{id: 1, parent_id: nil}.as_json.transform_keys { |k| k.camelize :lower }.to_json
=> '{"id":1,"parentId":null}'
```

It would be much shorter, if ruby allowed this:

```ruby
[1,2,16].map(&:to_s.(16))
=> ["1", "2", "10"]
# active_support example
{id: 1, parent_id: nil}.as_json.transform_keys(&:camelize.(:lower)).to_json
=> '{"id":1,"parentId":null}'
```

This can be implemented easily, by adding the `Symbol#call` method:

```ruby
class Symbol
  def call(*args, &block)
    ->(caller, *rest) { caller.send(self, *rest, *args, &block) }
  end
end

```

*Source*: [stackoverflow: Can you supply arguments to the map(&:method) syntax in Ruby?](http://stackoverflow.com/questions/23695653/can-you-supply-arguments-to-the-mapmethod-syntax-in-ruby)

**I think this is a rather common use case, so I propose to add `Symbol#call` to the Ruby standard library.**



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