---
title: "format(_:)"
framework: foundation
role: symbol
role_heading: Instance Method
path: "foundation/date/iso8601formatstyle/format(_:)"
---

# format(_:)

Creates a locale-aware ISO 8601 string representation from a date value.

## Declaration

```swift
func format(_ value: Date) -> String
```

## Parameters

- `value`: The date to format.

## Return Value

Return Value A string ISO 8601 representation of the date.

## Discussion

Discussion The format(_:) instance method generates a ISO 8601 formatted string from the provided date. Once you create a style, you can use it to format dates multiple times. In the following example, a format style is created to guide parsing a set of string representations of dates. Another format style is created and applied repeatedly to produce customized ISO 8601 string representations of those dates for a different locale. let input8601Format = Date.ISO8601FormatStyle()     .dateSeparator(.dash)     .year()     .month()     .day()

// Parse dates from strings using the input format defined above. let introDate01 = try? Date("2007-01-09", strategy: input8601Format) let introDate02 = try? Date("2010-01-27", strategy: input8601Format) let meetingDate2021 = try? Date("2021-06-07", strategy: input8601Format)

let outputFormat = Date.ISO8601FormatStyle() // define format style for string output     .locale(Locale(identifier: "en_US"))     .year()     .month()     .day()     .weekOfYear()

// Apply the output format to the three dates below. if let meet2021 = meetingDate2021 {     print(outputFormat.format(meet2021)) } // 202106W2301 if let intro02 = introDate02 {     print(outputFormat.format(intro02)) } // 201001W0403 if let intro01 = introDate01 {     print(outputFormat.format(intro01)) } // 200701W0202