Re-using variables in docker-compose yml

There are two articles describing using environment variable but my use case is different.

I have docker-compose file where I have 3-7 containers. Depends on situation.

version: '2'

services:
  db:
    image: example/db
  backend:
    image: example/server
  frontend:
    image: example/gui

Now, in above example all my images will use latest version, but I would like to control which version to deploy, therefore I want to define some variable version and use it in all my images, something like:

version: '2'

variable version=1.0.1

services:
  db:
    image: example/db:$version
  backend:
    image: example/server:$version
  frontend:
    image: example/gui:$version

Second example is wrong, but it shows my need what I want to achieve

Source: StackOverflow