Can any one explain the use of '&' in this piece of ruby code?

Question

s.feature_addons.select(&:is_active?)

It's just a shortcut for `s.feature_addons.select {|a| a.is_active?}`. You'll often see it with `map`, `inject`, and other methods, not just with `select`. | — Cary Swoveland, Oct 04 '13 at 06:08
The question that @not-rightfold linked to has a nicer discussion on that. — kristinalim, Oct 04 '13 at 06:14
@sawa provided a very good explanation [here](http://stackoverflow.com/questions/14881125/what-does-to-proc-method-mean). — Cary Swoveland, Oct 04 '13 at 06:35

score 5 · Accepted Answer · edited May 23 '17 at 11:50

5

It means:

s.feature_addons.select { |addon| addon.is_active? }

The & calls to_proc on the object, and passes it as a block to the method.

class Symbol
  def to_proc
    Proc.new { |*args| args.shift.__send__(self, *args) }
  end
end

U can define to_proc method in other classes: Examples

edited May 23 '17 at 11:50

Community

answered Oct 04 '13 at 06:05

Oleg Haidul

score 3 · Answer 2 · answered Oct 04 '13 at 06:05

That's a shortcut for to_proc. For example, the code you provided is the equivalent of:

s.feature_addons.select {|addon| addon.is_active?}

Some old documentation for it can be found here:

http://apidock.com/rails/Symbol/to_proc (when it was provided by ActiveSupport)

It then became a part of Ruby core in 1.9

score 1 · Answer 3 · answered Oct 04 '13 at 06:08

1

You can use this syntax as shorthand for methods to apply to an entire collection.

It is functionally the same as:

s.feature_addons.select { |a| a.is_active? }

You can use it with any collections, such as:

User.all.map(&:id)

etc

answered Oct 04 '13 at 06:08

Tyler

3 Answers3