Static variables in ruby, like in C functions

Question

Is there any such thing as static variables in Ruby that would behave like they do in C functions?

Here\'s a quick example of what I mean. It prints \"6\\n7\\n\" to the

Answer 1

You can use a global variable:

$a = 5
def test
  $a += 1
end

p test #=> 6
p test #=> 7

Answer 2

Similar to nicooga's answer but more self-contained:

def some_method
  @var ||= 0
  @var += 1
  puts @var
end

Answer 3

Scope your variable in a method and return lambda

def counter
  count = 0
  lambda{count = count+1}
end

test = counter
test[]
#=>1
test[]
#=>2

Answer 4

There is no syntactical equivalent to C's static variables in Ruby, and I've never seen something like that in languages with similar level of abstraction, like Javascript, Python, Elixir, etc.

What I understand about this C code is that the first time the function is called the compiler initializes the variable with the initial value. Subsequent calls will just get the current value of the varible.

This is how I would translate the same logic in ruby terms:

def test()
  @a ||= 5 # If not set, set it. We need to use an instance variable to persist the variable across calls.
  @a += 1 # sum 1 and return it's value
end

def main()
  puts test
  puts test
  0
end

This works outside a class too.

Answer 5

I think a standard way to do this is to use Fiber.

f = Fiber.new do
  a = 5
  loop{Fiber.yield a += 1}
end

puts f.resume # => 6
puts f.resume # => 7
...

Answer 6

Use a variable in the singleton class (The static class itself)

class Single
  def self.counter
    if @count  
      @count+=1
    else
      @count = 5
    end
  end
end

In ruby, any class is an object which has only one instance. Therefore, you can create an instance variable on the class, and it will work as a "static" method ;)

Output:

  ruby 2.5.5p157 (2019-03-15 revision 67260) [x86_64-linux]

=> :counter
   Single.counter
=> 5
   Single.counter
=> 6
   Single.counter
=> 7

To get this behaviour on the main scope, you can do:

module Countable
  def counter
    if @count  
      @count+=1
    else
      @count = 5
    end
  end
end

=> :counter
   self.class.prepend Countable # this "adds" the method to the main object
=> Object
   counter
=> 5
   counter
=> 6
   counter
=> 7