Difference between map and map object in terraform

Question

I was looking through the difference between map and object. My understanding is as follows :

A map can contain any type as long as all the elements are of the same type

variable "project_defaults" {
      type = map(string)
      default  = {
          project = "example_project"
          region = "eu-west-1" 
      }
    }

An object contains named attributes , each having their own type

variable "s3_buckets" {
  type = object({
    name       = string
    versioning = bool
    s3_rules   = list(map(any))
  })
  description = "List of maps for S3 buckets"
}

I have seen examples where map(object) is used but am really unsure what the difference is compared to the type object

variable "s3_buckets" {
      type = map(object({
        name                   = string
        versioning             = bool
        s3_rules   = list(map(any))
      }))
      description = "List of maps for S3 buckets"
    }

Am trying to make sense of when to make use of map(object) as opposed to using object . Syntax wise they look very similar but am unsure of the actual scenarios of when to use them.

Khajeh

Answer 1

A map can contain any type as long as all the elements are of the same type. This makes sense if I have a map of just strings and want to make use of the values for whatever resource configuration.

The schema for object types is { <KEY> = <TYPE>, <KEY> = <TYPE>, ... } — a pair of curly braces containing a comma-separated series of <KEY> = <TYPE> pairs. Values that match the object type must contain all the specified keys, and the value for each key must match its specified type. This makes sense if a specific structure of the object schema needs to be followed when creating a resource.

One thing to note is that a map (or a larger object) can be converted to an object if it has at least the keys required by the object schema. Any additional attributes are discarded during conversion, which means map -> object map conversions can be lossy.

Khajeh

Thanks to Terraform's implicit conversion, you can have map(string) or map(any) with string, number, and bool values. – Plasterwork

This answer has nothing to do with map(object) which is what you seem to be asking in your question. map(object) is just a map of objects, similar to how map(string) is a map of strings. You can also have things like map(map(string)) which is a map of maps of strings for example. map(object) isn't doing some sort of type conversion. – Extremely