CODEWITHSUNDEEP
terraform
Nick_Scott
Nick_Scott

Reputation: 107

Terraform: What is this =>

Im new to Terraform. I am going through a tutorial and cant determine what this does " => "

Below is an example output utilizing this feature.

output "for_output_map2" {
  description = "For Loop with Map - Advanced"
  value = {for c, instance in aws_instance.myec2vm: c => instance.public_dns}
}

What is the name of this feature ? What does it do ? Thank you.

Upvotes: 9

Views: 11568

Answers (4)

Michael Qin
Michael Qin

Reputation: 665

persons = {
  tom: { name: "Anthony" },
  amy: { name: "Amily" }
}

=> is the symbol to separate key and value for transformation purpose.

{ for k, v in persons: v.name => k }

Output:

{
  Anthony: "tom",
  Amily: "amy"
}

Upvotes: 1

RSW
RSW

Reputation: 1406

Simply put, the => is kind of "map element separator" in Terraform. It is used to define key-value pairs within a map. Using => you transform terraform map into another array or map for some purpose (e.g. using them for for_each Meta-Argument).

For example:

In snippet below, the for_each loop expression "${employee.name}${employee.id}@gmail.com" => employee is generating a map where the key is "${employee.name}${employee.id}@gmail.com" and the value is the employee object itself.

locals {
  # Array of Objects
  employees = [
    {
      name = "Alice"
      id   = 1234
      age  = 32
    },
    {
      name = "Bob"
      id   = 5678
      age  = 40
    }
  ]
}

resource "null_resource" "emp_directory" {
  for_each =  { for employee in local.employees : "${employee.name}${employee.id}@gmail.com" => employee } 
  provisioner "local-exec" {
    command = "echo Email ID ${each.key} belongs to ${each.value.name}"
  }
}

Output will be a map of maps. Notice how the key and value is transformed:

{
  "[email protected]" = {
    "age" = 32
    "id" = 1234
    "name" = "Alice"
  }
  "[email protected]" = {
    "age" = 40
    "id" = 5678
    "name" = "Bob"
  }
}

Terraform will perform the following actions:

  # null_resource.emp_directory["[email protected]"] will be created
  + resource "null_resource" "emp_directory" {
      + id = (known after apply)
    }

  # null_resource.emp_directory["[email protected]"] will be created
  + resource "null_resource" "emp_directory" {
      + id = (known after apply)
    }

Upvotes: 5

Paul Chuang
Paul Chuang

Reputation: 281

"=>" is a separator for one key and value pair inside an object.

For example, given a source object:

source = {
    1: {name: "foo", id: 1212},
    2: {name: "bar", id: 5656}
}

After this expression:

output "sample" {
    value = {for k, v in source: k => v.name}
}

The output will be:

{1: "foo", 2: " bar"}

Upvotes: 10

Martin Atkins
Martin Atkins

Reputation: 74789

This => symbol is not a distinct operator in its own right, but rather just one of the delimiters for the parts of this overall for expression:

  • for introduces the for expression, telling Terraform that this isn't just a normal object expression.
  • in separates the symbol declarations from the source collection value.
  • : separates the source collection value from the key expression.
  • => separates the key expression from the value expression.

for expressions can also have an if clause which follows the value expression, but there isn't one in the example you shared here. You can learn more about the if clause in Filtering Elements.

Upvotes: 8

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