---
title: "reserveCapacity(_:)"
framework: Swift
role: symbol
role_heading: Instance Method
platforms: [iOS 27.0+, iPadOS 27.0+, Mac Catalyst 27.0+, macOS 27.0+, tvOS 27.0+, visionOS 27.0+, watchOS 27.0+]
path: "swift/uniquearray/reservecapacity(_:)"
---

# reserveCapacity(_:)

Ensure that the array has capacity to store the specified number of elements, by growing its storage buffer if necessary.

## Declaration

```swift
mutating func reserveCapacity(_ n: Int)
```

## Discussion

Discussion If capacity < n, then this operation reallocates the unique array’s storage to grow it; on return, the array’s capacity becomes n. Otherwise the array is left as is. note: O(count)