83 lines
2.7 KiB
Markdown
83 lines
2.7 KiB
Markdown
---
|
|
layout: "language"
|
|
page_title: "Splat Expressions - Configuration Language"
|
|
---
|
|
|
|
# Splat Expressions
|
|
|
|
A _splat expression_ provides a more concise way to express a common
|
|
operation that could otherwise be performed with a `for` expression.
|
|
|
|
If `var.list` is a list of objects that all have an attribute `id`, then
|
|
a list of the ids could be produced with the following `for` expression:
|
|
|
|
```hcl
|
|
[for o in var.list : o.id]
|
|
```
|
|
|
|
This is equivalent to the following _splat expression:_
|
|
|
|
```hcl
|
|
var.list[*].id
|
|
```
|
|
|
|
The special `[*]` symbol iterates over all of the elements of the list given
|
|
to its left and accesses from each one the attribute name given on its
|
|
right. A splat expression can also be used to access attributes and indexes
|
|
from lists of complex types by extending the sequence of operations to the
|
|
right of the symbol:
|
|
|
|
```hcl
|
|
var.list[*].interfaces[0].name
|
|
```
|
|
|
|
The above expression is equivalent to the following `for` expression:
|
|
|
|
```hcl
|
|
[for o in var.list : o.interfaces[0].name]
|
|
```
|
|
|
|
Splat expressions are for lists only (and thus cannot be used [to reference resources
|
|
created with `for_each`](/docs/configuration/meta-arguments/for_each.html#referring-to-instances),
|
|
which are represented as maps in Terraform). However, if a splat expression is applied
|
|
to a value that is _not_ a list or tuple then the value is automatically wrapped in
|
|
a single-element list before processing.
|
|
|
|
For example, `var.single_object[*].id` is equivalent to `[var.single_object][*].id`,
|
|
or effectively `[var.single_object.id]`. This behavior is not interesting in most cases,
|
|
but it is particularly useful when referring to resources that may or may
|
|
not have `count` set, and thus may or may not produce a tuple value:
|
|
|
|
```hcl
|
|
aws_instance.example[*].id
|
|
```
|
|
|
|
The above will produce a list of ids whether `aws_instance.example` has
|
|
`count` set or not, avoiding the need to revise various other expressions
|
|
in the configuration when a particular resource switches to and from
|
|
having `count` set.
|
|
|
|
## Legacy (Attribute-only) Splat Expressions
|
|
|
|
An older variant of the splat expression is available for compatibility with
|
|
code written in older versions of the Terraform language. This is a less useful
|
|
version of the splat expression, and should be avoided in new configurations.
|
|
|
|
An "attribute-only" splat expression is indicated by the sequence `.*` (instead
|
|
of `[*]`):
|
|
|
|
```
|
|
var.list.*.interfaces[0].name
|
|
```
|
|
|
|
This form has a subtly different behavior, equivalent to the following
|
|
`for` expression:
|
|
|
|
```
|
|
[for o in var.list : o.interfaces][0].name
|
|
```
|
|
|
|
Notice that with the attribute-only splat expression the index operation
|
|
`[0]` is applied to the result of the iteration, rather than as part of
|
|
the iteration itself.
|