Feature #17663: Enumerator#with, an alternative to Enumerator#with_object

• Status: Open
• Assignee: -
• Target version: -

[RichOrElse (Ritchie Buitre)]

Enumerator#with yields each element along with the arguments

class Enumerator
  def with(*options)
    return to_enum(:with, *options) unless defined? yield

    each do |entry|
      yield entry, *options
    end
  end
end

Suppose we have a proc that accepts more than 1 argument.

format = proc do |value, *option|
  value.to_s(*option)
end

Normally to apply the argument we enclosed it in a block, like so:

(10..15).map { |n| format.(n, 16) } # => ["a", "b", "c", "d", "e", "f"]

I found Enumerator#with_object method awkward to use.

(10..15).each.with_object(16).map(&format) # => ["a", "b", "c", "d", "e", "f"]

Tried simplifying this code further, but Enumerator#with_object ignores the given block and just returns the argument.

(10..15).map.with_object(16, &format) # => 16

Compare to how concise this line using Enumerator#with

(10..15).map.with(16, &format)  # => ["a", "b", "c", "d", "e", "f"]

[RichOrElse (Ritchie Buitre)]

• Description updated (diff)

[RichOrElse (Ritchie Buitre)]

• Subject changed from Enumerator#with, an alternative for Enumerator#with_object to Enumerator#with, an alternative to Enumerator#with_object

[RichOrElse (Ritchie Buitre)]

• Description updated (diff)

[Hanmac (Hans Mackowiak)]

i had a similar problem when i wanted to make Symbol to_proc use parameters, i would have done something like :to_s.(16)

for your list of code comparisons:

(10..15).map(&"%x".method(:%))

[RichOrElse (Ritchie Buitre)]

Hanmac (Hans Mackowiak) wrote in #note-4:

i had a similar problem when i wanted to make Symbol to_proc use parameters, i would have done something like :to_s.(16)

Thanks, the implementation of format proc could be anything other than Integer#to_s.
I usually define to_proc for my classes, in those scenarios I couldn't use Symbol#call, which is not intended for specifying the second parameter without the first.

class UserPresenter < SimpleDelegator
  def initialize(model, view = nil)
    @view = view
    super(model)
  end

  def self.to_proc
    method(:new).to_proc
  end
end

# in a controller action
@users = User.all.map.with(view_context, &UserPresenter)