Format For Expressions and Comprehensions

Formatting For Expressions

Terraform's for expressions create lists and maps from existing collections. They can range from simple one-liners to complex multi-line expressions with filtering conditions.

Simple For Expressions

locals {
  upper_names = [for name in var.names : upper(name)]

  name_map = {
    for name in var.names : name => upper(name)
  }

  filtered = [
    for name in var.names : upper(name)
    if length(name) > 3
  ]
}

Complex For Expressions

locals {
  subnet_config = {
    for idx, cidr in var.subnet_cidrs : "subnet-${idx}" => {
      cidr_block        = cidr
      availability_zone = var.azs[idx % length(var.azs)]
      is_public         = idx < var.public_subnet_count
    }
  }

  flattened_rules = flatten([
    for sg_name, sg_rules in var.security_groups : [
      for rule in sg_rules : {
        sg_name   = sg_name
        from_port = rule.from_port
        to_port   = rule.to_port
        protocol  = rule.protocol
      }
    ]
  ])

  tagged_resources = {
    for key, resource in local.all_resources : key => merge(
      resource,
      {
        tags = merge(local.common_tags, resource.tags)
      }
    )
  }
}

Formatting Rules

• Single-line: Simple for expressions that fit on one line stay inline: [for x in list : transform(x)]
• Multi-line with filter: When a if condition is added, the filter goes on its own line
• Nested for: Each nested for gets its own indentation level
• Map output: key => value pairs in map for expressions align their => operators
• Complex values: When the output value is an object, it gets its own indented block