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# `Fn::Length`
<a name="intrinsic-function-reference-length"></a>

The intrinsic function `Fn::Length` returns the number of elements within an array or an intrinsic function that returns an array.

**Important**  
You must use the [`AWS::LanguageExtensions` transform](transform-aws-languageextensions.md) to use the `Fn::Length` intrinsic function.

## Declaration
<a name="length-declaration"></a>

### JSON
<a name="intrinsic-function-reference-length-syntax.json"></a>

```
{ "Fn::Length" : IntrinsicFunction }
```

```
{ "Fn::Length" : Array }
```

### YAML
<a name="intrinsic-function-reference-length-syntax.yaml"></a>

```
Fn::Length : IntrinsicFunction
```

```
Fn::Length : Array
```

## Parameters
<a name="length-parameters"></a>

`IntrinsicFunction`  
The intrinsic function that returns an array that you want to return a number of elements from.

`Array`  
The array you want to return the number of elements from.

## Return value
<a name="intrinsic-function-reference-length-return"></a>

The number of elements in the intrinsic function that returns an array or in the array passed to the intrinsic function. 

## Examples
<a name="intrinsic-function-reference-length-examples"></a>

### Return the number of elements in an intrinsic function that returns an array
<a name="intrinsic-function-reference-length-example-subsection"></a>

This example snippet returns the number of elements in an intrinsic function that returns an array. The function returns 3.

#### JSON
<a name="intrinsic-function-reference-length-example.json"></a>

```
{
//...
    "Transform": "AWS::LanguageExtensions"
    //...
        "Fn::Length" : {
            "Fn::Split": ["|", "a|b|c"]
        }
//...
}
```

#### YAML
<a name="intrinsic-function-reference-legnth-example.yaml"></a>

```
Transform: 'AWS::LanguageExtensions'
#...
  Fn::Length: 
    !Split ["|", "a|b|c"]
#...
```

### Return the number of elements in a Ref intrinsic function that refers to a list parameter type
<a name="intrinsic-function-reference-length-example2"></a>

This example snippet returns the number of elements in a `Ref` intrinsic function that refers to a list parameter type. If the parameter with the name `ListParameter` is a list with 3 elements, the function returns 3.

#### JSON
<a name="intrinsic-function-reference-length-example2.json"></a>

```
{
//...
    "Transform": "AWS::LanguageExtensions"
    //...
        "Fn::Length": {
            "Ref": "ListParameter"
        }
//...
}
```

#### YAML
<a name="intrinsic-function-reference-legnth-example2.yaml"></a>

```
Transform: 'AWS::LanguageExtensions'
#...
  Fn::Length: 
    !Ref ListParameter
#...
```

### Return the number of elements in an array
<a name="intrinsic-function-reference-length-example3"></a>

This example snippet returns the number of elements in the array passed to the intrinsic function. The function returns 3.

#### JSON
<a name="intrinsic-function-reference-length-example3.json"></a>

```
 1. {
 2. //...
 3.     "Transform": "AWS::LanguageExtensions"
 4.     //...
 5.         "Fn::Length": [
 6.             1,
 7.             {"Ref": "ParameterName"}, 
 8.             3
 9.         ]
10. //...
11. }
```

#### YAML
<a name="intrinsic-function-reference-legnth-example3.yaml"></a>

```
Transform: 'AWS::LanguageExtensions'
#...
  Fn::Length: 
    - 1
    - !Ref ParameterName
    - 3
#...
```

## Supported functions
<a name="length-supported-functions"></a>

You can use the following functions in the `Fn::Length` intrinsic function or array:
+ `Condition Functions`
+ `Fn::Base64`
+ `Fn::FindInMap`
+ `Fn::Join`
+ `Fn::Length`
+ `Fn::Select`
+ `Fn::Split`
+ `Fn::Sub`
+ `Fn::ToJsonString`
+ `Ref`