Traversing Nested Maps

Terraform used to use splat expressions for this stuff (and I wish they still worked), but now this is all done with for expressions.

Using your example code as a guide, it's pretty straightforward to select the structure of the map where the address_space lists are the first element down, like this:

> local.subscriptions.MySecondSubcription.VirtualNetworks
{
  "vNet1" = {
    "address_space" = [
      "10.20.0.0/24",
      "192.168.3.0/24",
    ]
  }
  "vNet2" = {
    "address_space" = [
      "10.30.0.0/24",
      "192.168.4.0/24",
    ]
  }
}

Now, using the for expression, we can cherry pick the address_space into a list by iterating over that level of the map like this:

> [ for net in local.subscriptions.MySecondSubcription.VirtualNetworks : net.address_space ]
[
  [
    "10.20.0.0/24",
    "192.168.3.0/24",
  ],
  [
    "10.30.0.0/24",
    "192.168.4.0/24",
  ],
]

If the subdivided lists aren't helpful, you can flatten() the output:

> flatten([ for net in local.subscriptions.MySecondSubcription.VirtualNetworks : net.address_space ])
[
  "10.20.0.0/24",
  "192.168.3.0/24",
  "10.30.0.0/24",
  "192.168.4.0/24",
]

Credits

Inspired by the question in this Reddit thread.