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Some docs updates to clarify splat confusion

This commit is contained in:
Pam Selle 2019-10-01 11:25:57 -04:00
parent dcb65fa9c7
commit 67e314dcbe
2 changed files with 17 additions and 8 deletions
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23
website/docs/configuration/expressions.html.md
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@ -22,8 +22,8 @@ and a number of built-in functions.
Expressions can be used in a number of places in the Terraform language,
but some contexts limit which expression constructs are allowed,
such as requiring a literal value of a particular type or forbidding
references to resource attributes. Each language feature's documentation
describes any restrictions it places on expressions.
[references to resource attributes](/docs/configuration/expressions.html#references-to-resource-attributes).
Each language feature's documentation describes any restrictions it places on expressions.
You can experiment with the behavior of Terraform's expressions from
the Terraform expression console, by running
@ -171,6 +171,9 @@ The following named values are available:
If the resource has the `count` argument set, the value of this expression
is a _list_ of objects representing its instances.
If the resource has the `for_each` argument set, the value of this expression
is a _map_ of objects representing its instances.
For more information, see
[references to resource attributes](#references-to-resource-attributes) below.
* `var.<NAME>` is the value of the
@ -183,7 +186,8 @@ The following named values are available:
* `data.<DATA TYPE>.<NAME>` is an object representing a
[data resource](./data-sources.html) of the given data
source type and name. If the resource has the `count` argument set, the value
is a list of objects representing its instances.
is a list of objects representing its instances. If the resource has the `for_each`
argument set, the value is a map of objects representing its instances.
* `path.module` is the filesystem path of the module where the expression
is placed.
* `path.root` is the filesystem path of the root module of the configuration.
@ -581,11 +585,14 @@ The above expression is equivalent to the following `for` expression:
[for o in var.list : o.interfaces[0].name]
```
Splat expressions also have another useful effect: if they are applied to
a value that is _not_ a list or tuple then the value is automatically wrapped
in a single-element list before processing. That is, `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,
Splat expressions are for lists only (and thus cannot be used [to reference resources
created with `for_each`](/docs/configuration/resources.html#referring-to-instances-1),
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:

2
website/docs/configuration/resources.html.md
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@ -370,6 +370,8 @@ identified by a map key (or set member) from the value provided to `for_each`.
- `<TYPE>.<NAME>` (for example, `azurerm_resource_group.rg`) refers to the resource block.
- `<TYPE>.<NAME>[<KEY>]` (for example, `azurerm_resource_group.rg["a_group"]`,
`azurerm_resource_group.rg["another_group"]`, etc.) refers to individual instances.
- `{ for key, value in <TYPE>.<NAME> : key => value.public_ip }`, an expression referring to instances
in a resource managed with `for_each`
This is different from resources without `count` or `for_each`, which can be
referenced without an index or key.