---
title: "overlay(blockCount:)"
framework: diskimagekit
role: symbol
role_heading: Type Method
path: "diskimagekit/diskimage/layertype-swift.struct/overlay(blockcount:)"
---

# overlay(blockCount:)

An overlay layer with a specific block count.

## Declaration

```swift
static func overlay(blockCount: Int) -> DiskImage.LayerType
```

## Parameters

- `blockCount`: The number of blocks for the overlay layer, which changes the effective size of the entire stack. blockCount must be greater than zero.

## Discussion

Discussion Overlay layers store all the changed blocks from the layers beneath it in the stack. This variant resizes the stacked disk image since the size is determined by the top-most layer.