'pass parameter by reference' in Ruby?

In Ruby, is it possible to pass by reference a parameter with value-type semantics (e.g. a Fixnum)?
I'm looking for something similar to C#'s '**ref**' keyword.

Example:

def func(x)
x += 1
end

a = 5
func(a) #this should be something like func(ref a)
puts a #should read '6'

Btw. I know I could just use:

a = func(a)

However, it seems that composite objects, like hashes, are passed by reference:

fp = {}
def changeit(par)
par[:abc] = 'cde'
end

changeit(fp)

p fp

gives

{:abc=>"cde"}

You can try following trick:

def func(x)
x[0] += 1
end

a = [5]
func(a) #this should be something like func(ref a)
puts a[0] #should read '6'

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> Fixnum objects have immediate value. This means that when they are assigned or
passed as parameters, the actual object is passed, rather than a reference to
that object.

Also [Ruby is pass by value][1].


[1]:

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Ruby doesn't support "pass by reference" at all. Everything is an object and the references to those objects are always passed by value. Actually, in your example you are passing a copy of the reference to the `Fixnum` Object by value.

The problem with the your code is, that `x += 1` doesn't modify the passed `Fixnum` Object but instead creates a completely new and independent object.

I think, Java programmers would call `Fixnum` objects **immutable**.

You can accomplish this by explicitly passing in the current binding:

def func(x, bdg)
eval "#{x} += 1", bdg
end

a = 5
func(:a, binding)
puts a # => 6

In Ruby you can't pass parameters by reference. For your example, you would have to return the new value and assign it to the variable a or create a new class that contains the value and pass an instance of this class around. Example:

class Container
attr_accessor :value
def initialize value
@value = value
end
end

def func(x)
x.value += 1
end

a = Container.new(5)
func(a)
puts a.value