Ruby function as value of hash

Question

I was wondering if or how it is possible to map a function to a value of a hash.

For example: ----Start Class------------

def foo(var)
    return var + 2
end

hash_var = { func => foo() }

----End Class--------------

so that I could later call

Class::hash_var["func"][10]

or

Class::hash_var["func"](10)

and that would return 12?

score 10 · Answer 1 · edited Oct 23 '12 at 15:40

10

You could use method method.

def foo(var)
      return var + 2
end

hash_var = { :func => method(:foo) }

hash_var[:func].call(10)

edited Oct 23 '12 at 15:40

John Douthat

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answered Oct 23 '12 at 15:26

xdazz

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score 4 · Accepted Answer · answered Oct 23 '12 at 16:01

Functions/methods are one of the few things in Ruby that are not objects, so you can't use them as keys or values in hashes. The closest thing to a function that is an object would be a proc. So you are best off using these...

The other answers pretty much listed all possible ways of how to put a proc into a hash as value, but I'll summarize it nonetheless ;)

hash = {}

hash['variant1'] = Proc.new {|var| var + 2}
hash['variant2'] = proc     {|var| var + 2}
hash['variant3'] = lambda   {|var| var + 2}

def func(var)
  var + 2
end

hash['variant4'] = method(:func) # the *method* method returns a proc
                                 # describing the method's body

there are also different ways to evaluate procs:

hash['variant1'].call(2) # => 4
hash['variant1'][2]      # => 4
hash['variant1'].(2)     # => 4

score 3 · Answer 3 · answered Oct 23 '12 at 15:24

3

You can set the value to a Proc and call it.

hash_var = {
  'func' =>  proc {|x| x+2}
}

hash_var['func'].call(10) #=> 12

answered Oct 23 '12 at 15:24

John Douthat

40,711
10
69
66

score 2 · Answer 4 · answered Oct 23 '12 at 15:27

2

Try using lambdas

hash_var = { :func => lambda { |var| var + 2 }}
hash_var['func'].call(5) #=> 7

answered Oct 23 '12 at 15:27

Raghu

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The lambda method has the same effect as the proc method; they both yield Proc objects containing the provided block. – John Douthat Oct 23 '12 at 15:29
Yup , i know !! I did not see the proc answer before i posted my answer !! – Raghu Oct 23 '12 at 15:30

score 0 · Answer 5 · answered Apr 03 '19 at 17:59

Another option would be:

def foo(name)
    puts "Hi #{name}"
end

def bar(numb)
    puts numb + 1
end

hash_var = { func: :foo, func2: :bar }
send hash_var[:func], "Grid"
# => Hi Grid
send hash_bar[:func2], 3
# => 4

Here is some information about the #send method What does send() do in Ruby?

Ruby function as value of hash

5 Answers5