The ampersand operator with parameters

Question

I wonder, isn't it possible to call a method using & operator with parameters?

items.each &:my_proc # ok
items.each &:my_proc(123, "456") # ops!

score 7 · Accepted Answer · answered Jul 24 '13 at 10:21

7

No, it's not possible. Use full form.

items.each{|i| i.my_proc(123, '456')}

Look at the source of Symbol#to_proc for the "why".

answered Jul 24 '13 at 10:21

Sergio Tulentsev

looked, but didn't find the reason why. would you mind explaining it? – Alan Coromano Jul 24 '13 at 11:59
1

@MariusKavansky: Because it's not implemented :) – Sergio Tulentsev Jul 24 '13 at 12:01

Patrick Oscity · Answer 2 · 2013-07-24T10:53:19.533

3

You can use a bit of trickery and acheive something similar:

class Symbol
  def [](*args)
    proc{|obj| obj.send(self, *args) }
  end
end

[123.456, 234.567].map(&:round[2])
#=> [123.46, 234.57]

I highly discourage the use in production code though, since gems etc may rely on Symbol#[]. This is just a fun thing to play around with ;-)

edited Jul 24 '13 at 10:53

answered Jul 24 '13 at 10:47

Patrick Oscity

Nice. You could use, e.g., `bind_args` instead of `[]`. Although not as pretty to use, it'd be safer in production code. – Wayne Conrad Jul 24 '13 at 10:58
1

That's true. But then again i prefer standards over magic and the form suggested by @SergioTulentsev is better suited. – Patrick Oscity Jul 24 '13 at 12:10
1

Actually `map{|x| x.round(2)}` is even shorter and better to read than `map(&:round.bind_args(2))` :) – Patrick Oscity Jul 24 '13 at 15:02

2 Answers2