For

About

With for loops you can iterate through a list, a set, a tuple, a map, or an object.

for loops can produce different results depending on how they are declared, the type of brackets decide the result type.

It’s important to know that for loops are used to manipulate and transform values and not delegate the creation of N instances of a resource - we use the count or for_each argument to achieve that.

Declaring a for loop that produces a tuple #

Here we’re storing the names coming from a data source into a local named regions using a for loop.

data "aws_regions" "available" {}

locals {
  regions = [for name in data.aws_regions.available.names : name]
}

Optionally we could extract the index from the for loop using a second symbol right after the for keyword.

data "aws_regions" "available" {}

locals {
  regions_indices = [for index, name in data.aws_regions.available.names : index]
}

In the above example, regions_indices its value is a tuple containing the indices (0, 1, 2, etc) of the region names.

Declaring a for loop that produces an object #

If we use curly braces to annotate our for loop, we produce an object. When producing an object we must provide an additional expression using =>, this constructs the values of the object for each key we iterate through.

locals {
  numbers         = [2, 4, 6]
  squared_numbers = {for number in local.numbers : number => number * number}
}

The above example produces the following object:

$ terraform console
> local.squared_numbers
{
  "2" = 4
  "4" = 16
  "6" = 36
}

Declare a for loop that filters out elements #

Optionally you can include an if clause in the for loop to filter out elements.

data "aws_regions" "available" {}

locals {
  regions = [for name in data.aws_regions.available.names : name if != ""]
}

Want to learn more about For loops? Check out the docs.

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