---
layout: "language"
page_title: "Types and Values - Configuration Language"
---

# Types and Values

The result of an expression is a _value_. All values have a _type_, which
dictates where that value can be used and what transformations can be
applied to it.

## Types

The Terraform language uses the following types for its values:

* `string`: a sequence of Unicode characters representing some text, like
  `"hello"`.
* `number`: a numeric value. The `number` type can represent both whole
  numbers like `15` and fractional values like `6.283185`.
* `bool`: a boolean value, either `true` or `false`. `bool` values can be used in conditional
  logic.
* `list` (or `tuple`): a sequence of values, like
  `["us-west-1a", "us-west-1c"]`. Elements in a list or tuple are identified by
  consecutive whole numbers, starting with zero.
* `map` (or `object`): a group of values identified by named labels, like
  `{name = "Mabel", age = 52}`.

Strings, numbers, and bools are sometimes called _primitive types._ Lists/tuples and maps/objects are sometimes called _complex types,_ _structural types,_ or _collection types._

Finally, there is one special value that has _no_ type:

* `null`: a value that represents _absence_ or _omission._ If you set an
  argument of a resource or module to `null`, Terraform behaves as though you
  had completely omitted it — it will use the argument's default value if it has
  one, or raise an error if the argument is mandatory. `null` is most useful in
  conditional expressions, so you can dynamically omit an argument if a
  condition isn't met.

## Literal Expressions

A _literal expression_ is an expression that directly represents a particular
constant value. Terraform has a literal expression syntax for each of the value
types described above.

### Strings

Strings are usually represented by a double-quoted sequence of Unicode
characters, `"like this"`. There is also a "heredoc" syntax for more complex
strings.

String literals are the most complex kind of literal expression in
Terraform, and have their own page of documentation. See [Strings](./strings.html)
for information about escape sequences, the heredoc syntax, interpolation, and
template directives.

### Numbers

Numbers are represented by unquoted sequences of digits with or without a
decimal point, like `15` or `6.283185`.

### Bools

Bools are represented by the unquoted symbols `true` and `false`.

### Null

The null value is represented by the unquoted symbol `null`.

### Lists/Tuples

Lists/tuples are represented by a pair of square brackets containing a
comma-separated sequence of values, like `["a", 15, true]`.

List literals can be split into multiple lines for readability, but always
require a comma between values. A comma after the final value is allowed,
but not required. Values in a list can be arbitrary expressions.

### Maps/Objects

Maps/objects are represented by a pair of curly braces containing a series of
`<KEY> = <VALUE>` pairs:

```hcl
{
  name = "John"
  age  = 52
}
```

Key/value pairs can be separated by either a comma or a line break.

The values in a map
can be arbitrary expressions.

The keys in a map must be strings; they can be left unquoted if
they are a valid [identifier](/docs/configuration/syntax.html#identifiers), but must be quoted
otherwise. You can use a non-literal string expression as a key by wrapping it in
parentheses, like `(var.business_unit_tag_name) = "SRE"`.

## Indices and Attributes

[inpage-index]: #indices-and-attributes

Elements of list/tuple and map/object values can be accessed using
the square-bracket index notation, like `local.list[3]`. The expression within
the brackets must be a whole number for list and tuple values or a string
for map and object values.

Map/object attributes with names that are valid identifiers can also be accessed
using the dot-separated attribute notation, like `local.object.attrname`.
In cases where a map might contain arbitrary user-specified keys, we recommend
using only the square-bracket index notation (`local.map["keyname"]`).

## More About Complex Types

In most situations, lists and tuples behave identically, as do maps and objects.
Whenever the distinction isn't relevant, the Terraform documentation uses each
pair of terms interchangeably (with a historical preference for "list" and
"map").

However, module authors and provider developers should understand the
differences between these similar types (and the related `set` type), since they
offer different ways to restrict the allowed values for input variables and
resource arguments.

For complete details about these types (and an explanation of why the difference
usually doesn't matter), see [Type Constraints](/docs/configuration/types.html).

## Type Conversion

Expressions are most often used to set values for the arguments of resources and
child modules. In these cases, the argument has an expected type and the given
expression must produce a value of that type.

Where possible, Terraform automatically converts values from one type to
another in order to produce the expected type. If this isn't possible, Terraform
will produce a type mismatch error and you must update the configuration with a
more suitable expression.

Terraform automatically converts number and bool values to strings when needed.
It also converts strings to numbers or bools, as long as the string contains a
valid representation of a number or bool value.

* `true` converts to `"true"`, and vice-versa
* `false` converts to `"false"`, and vice-versa
* `15` converts to `"15"`, and vice-versa

