[ruby-core:83139] [Ruby trunk Feature#12115] Add Symbol#call to allow to_proc shorthand with arguments

Issue #12115 has been updated by jwmittag (J旦rg W Mittag).


knu (Akinori MUSHA) wrote:
> Wouldn't Array#to_proc make sense?
> 
> ```ruby
> class Array
>   def to_proc
>     proc { |x| x.__send__(*self) }
>   end
> end
> 
> [100, 200, 300].map(&[:to_s, 16])
> # => ["64", "c8", "12c"]
> ```

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`.

See #11653 (`Hash#to_proc`) for what I mean, and #11262 for a more comprehensive argument.

----------------------------------------
Feature #12115: Add Symbol#call to allow to_proc shorthand with arguments
https://bugs.ruby-lang.org/issues/12115#change-67081

* Author: felixbuenemann (Felix B端nemann)
* 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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