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| layout | page_title |
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| language | 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:
[for o in var.list : o.id]
This is equivalent to the following splat expression:
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:
var.list[*].interfaces[0].name
The above expression is equivalent to the following for expression:
[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,
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:
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.