84 lines
3.1 KiB
Markdown
84 lines
3.1 KiB
Markdown
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---
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title: Assignment and scope
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description: An assignment binds an identifier to a variable, option, or function. Every identifier in a program must be assigned.
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menu:
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flux_v0_ref:
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parent: Flux specification
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name: Assignment and scope
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weight: 108
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aliases:
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- /influxdb/v2/reference/flux/language/assignment-scope/
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- /influxdb/cloud/reference/flux/language/assignment-scope/
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---
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An assignment binds an identifier to a variable, option, or function.
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Every identifier in a program must be assigned.
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Flux is lexically scoped using blocks:
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1. The scope of a preassigned identifier is in the universe block.
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2. The scope of an identifier denoting a variable, option, or function at the top level (outside any function) is the package block.
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3. The scope of the name of an imported package is the file block of the file containing the import declaration.
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4. The scope of an identifier denoting a function argument is the function body.
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5. The scope of an identifier assigned inside a function is the innermost containing block.
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An identifier assigned in a block may be reassigned in an inner block with the exception of option identifiers.
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While the identifier of the inner assignment is in scope, it denotes the entity assigned by the inner assignment.
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Note that the package clause is not an assignment.
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The package name does not appear in any scope.
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Its purpose is to identify the files belonging to the same package and to specify the default package name for import declarations.
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## Variable assignment
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A variable assignment creates a variable bound to an identifier and gives it a type and value.
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A variable keeps the same type and value for the remainder of its lifetime.
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An identifier assigned to a variable in a block cannot be reassigned in the same block.
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An identifier can be reassigned or shadowed in an inner block.
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```js
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VariableAssignment = identifier "=" Expression .
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```
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##### Examples of variable assignment
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{{% note %}}
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In this code snippet, `n` and `m` are defined in an outer block as integers. Within the anonymous function, `n` and `m` are defined as strings, but only within that scope. So while the function will return `"ab"`, `n` and `m` in the outer scope are unchanged, remaining `n = 1` and `m = 2`.
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{{% /note %}}
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```js
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n = 1
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m = 2
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x = 5.4
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f = () => {
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n = "a"
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m = "b"
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return n + m
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}
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```
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## Option assignment
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```js
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OptionAssignment = "option" [ identifier "." ] identifier "=" Expression .
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```
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An option assignment creates an option bound to an identifier and gives it a type and a value.
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Options may only be assigned in a package block.
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Once declared, an option may not be redeclared in the same package block.
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An option declared in one package may be reassigned a new value in another.
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An option keeps the same type for the remainder of its lifetime.
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###### Examples
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```js
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// alert package
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option severity = ["low", "moderate", "high"]
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// foo package
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import "alert"
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option alert.severity = ["low", "critical"] // qualified option
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option n = 1
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option n = 2
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f = (a, b) => a + b + n
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x = f(a:1, b:1) // x = 4
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```
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{{< page-nav prev="/flux/v0/spec/blocks/" next="/flux/v0/spec/expressions/" >}}
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