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