---
title: "appendInterpolation(dayOfYear:)"
framework: foundation
role: symbol
role_heading: Instance Method
path: "foundation/date/formatstring/stringinterpolation/appendinterpolation(dayofyear:)"
---

# appendInterpolation(dayOfYear:)

## Declaration

```swift
mutating func appendInterpolation(dayOfYear: Date.FormatStyle.Symbol.DayOfYear)
```