---
title: "map(_:)"
framework: swift
role: symbol
role_heading: Instance Method
path: "swift/optional/map(_:)"
---

# map(_:)

Evaluates the given closure when this Optional instance is not nil, passing the unwrapped value as a parameter.

## Declaration

```swift
func map<E, U>(_ transform: (Wrapped) throws(E) -> U) throws(E) -> U? where E : Error, U : ~Copyable
```

## Parameters

- `transform`: A closure that takes the unwrapped value of the instance.

## Return Value

Return Value The result of the given closure. If this instance is nil, returns nil.

## Discussion

Discussion Use the map method with a closure that returns a non-optional value. This example performs an arithmetic operation on an optional integer. let possibleNumber: Int? = Int("42") let possibleSquare = possibleNumber.map { $0 * $0 } print(possibleSquare) // Prints "Optional(1764)"

let noNumber: Int? = nil let noSquare = noNumber.map { $0 * $0 } print(noSquare) // Prints "nil"

## See Also

### Transforming an Optional Value

- [flatMap(_:)](swift/optional/flatmap(_:).md)