How do I reference a function in Ruby?

Question

In python, it\'s fairly straightforward to reference a function:

>>> def foo():
...     print \"foo called\"
...     return 1
... 
>>> x =          


        

Answer 1

The (main) difference between functions and methods as copied from https://stackoverflow.com/a/26620095/226255

Functions are defined outside of classes, while methods are defined inside of and part of classes.

Ruby does not have functions and your def foo ends up being a method for the Object class.

If you insist on defining foo like you're doing above, you can extract its "functionality" by doing this:

def foo(a,b)
 a+b
end

x = method(:foo).to_proc
x.call(1,2)
=> 3

Explanation:

> method(:foo) # this is Object.method(:foo), returns a Method object bound to 
# object of type 'Class(Object)'
=> #

method(:foo).to_proc
# a Proc that can be called without the original object the method was bound to
=> #

Important note:

to_proc "copies" the method's object's associated instance variables if any. Consider this:

class Person
  def initialize(name)
    @name = name
  end

  def greet
    puts "hello #{@name}"
  end
end

greet = Person.new('Abdo').method(:greet) 
# note that Person.method(:greet) returns an UnboundMethod and cannot be called 
# unless you bind it to an object

> greet.call
hello Abdo
=> nil

Conceptually, if you want a "function" that would work on a certain type of objects, it should be a method and you should organize your code as such. If you only need your "function" in a certain context and wish to pass it around, use lambdas:

greet = lambda { |person| "hello #{person}" }
yell_at = lambda { |person| "HELLO #{person.upcase}" }

def do_to_person(person, m)
  m.call(person)
end

do_to_person('Abdo', greet)