[ruby-core:74065] [Ruby trunk Feature#12115] Add Symbol#call to allow to_proc shorthand with arguments

Issue #12115 has been updated by Robert A. Heiler.


I think there have been many other similar proposals. Nobu linked to other
discussions.

From what I have seen, I think the major problem is coming up with a nice
syntax proposal.

`.map(&:foo)`

is ok because it is short.

Adding implicit arguments to it is harder.

`[1,2,16].map(&:to_s(16))`

Is probably ok. But I am not sure if the parser is happy with it.

`[1,2,16].map(&:to_s.(16))`

Is not good IMHO, the . there is very confusing for me.

There is a slight alternative to .call() which is the []

I like [] a lot, but I think it looks a bit weird too 
inside of ().

Perhaps we do not have a syntax that will be better if
we require arguments for &: ?

----------------------------------------
Feature #12115: Add Symbol#call to allow to_proc shorthand with arguments
https://bugs.ruby-lang.org/issues/12115#change-57217

* Author: Felix B端nemann
* Status: Open
* Priority: Normal
* Assignee: 
----------------------------------------
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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