reference to a method on an object

Question

I have asked a similar question earlier: reference to a method?

but now I am trying to figure out how to do this with this code:

arr0 = [1,2,3]
arr1 = [2,3,4,5]
arr1.reject! {|x|
    arr0.include? x
}

apparently {|x| arr0.include? x} can be simplified to just arr0.include?. But I do not know how to get this method reference.

EDIT: I am not interested in how to subtract arrays in Ruby using a simpler syntax. I am looking for a way to get a reference to a method.

score 6 · Answer 1 · answered Sep 28 '12 at 16:22

6

arr1.reject!(&arr0.method(:include?))

answered Sep 28 '12 at 16:22

Jörg W Mittag

@steenslag: The ampersand in a *parameter list* means "wrap this block in a `Proc`". The ampersand in an *argument list* means "unwrap this `Proc` into a block (and call `to_proc` on it first, if it isn't already a block)". `Method` implements `to_proc`, just like `Symbol` does, so, it works exactly the same way as it does with `Symbol`s. – Jörg W Mittag Sep 30 '12 at 22:23

InternetSeriousBusiness · Answer 2 · 2012-09-28T15:40:14.103

1

You can do that with

arr1 - arr0

and you can't do that with a pretzel colon, because you have an argument.

edited Sep 28 '12 at 15:40

answered Sep 28 '12 at 15:33

yes, I can do that with this syntax. my question is how to get the method in the sample code that I posted. – akonsu Sep 28 '12 at 15:34
arr1 -= arr0 since reject! modifies the receiver. – Sep 28 '12 at 15:35
:) thanks. I did not mean to say that I want to use pretzel column necessarily. – akonsu Sep 28 '12 at 15:41

score 1 · Accepted Answer · answered Sep 28 '12 at 16:21

1

Each Object in Ruby has a method method:

m = [1,2,3].method(:include?) #reference to the include? method of this array.
p m.call(1) #call the method with an argument ; => true

answered Sep 28 '12 at 16:21

steenslag

score 1 · Answer 4 · answered Sep 28 '12 at 16:36

1

arr0 = [1,2,3]
arr1 = [2,3,4,5]

m = arr0.method(:include?)
arr1.reject!(&m) #=> [4, 5]

answered Sep 28 '12 at 16:36

megas

4 Answers4