# The DateTimeInterface interface

(PHP 5 >= 5.5.0, PHP 7, PHP 8)

## Introduction

DateTimeInterface was created so that parameter, return, or property type declarations may accept either DateTimeImmutable or DateTime as a value. It is not possible to implement this interface with userland classes.

Common constants that allow for formatting DateTimeImmutable or DateTime objects through DateTimeImmutable::format() and DateTime::format() are also defined on this interface.

## Interface synopsis

interface DateTimeInterface {
/* Constants */
public const string ATOM = "Y-m-d\\TH:i:sP";
public const string COOKIE = "l, d-M-Y H:i:s T";
public const string ISO8601 = "Y-m-d\\TH:i:sO";
public const string ISO8601_EXPANDED = "X-m-d\\TH:i:sP";
public const string RFC822 = "D, d M y H:i:s O";
public const string RFC850 = "l, d-M-y H:i:s T";
public const string RFC1036 = "D, d M y H:i:s O";
public const string RFC1123 = "D, d M Y H:i:s O";
public const string RFC7231 = "D, d M Y H:i:s \\G\\M\\T";
public const string RFC2822 = "D, d M Y H:i:s O";
public const string RFC3339 = "Y-m-d\\TH:i:sP";
public const string RFC3339_EXTENDED = "Y-m-d\\TH:i:s.vP";
public const string RSS = "D, d M Y H:i:s O";
public const string W3C = "Y-m-d\\TH:i:sP";
/* Methods */
public diff(DateTimeInterface `$targetObject`, bool `$absolute` = `false`): DateInterval
public format(string `$format`): string
public getOffset(): int
public getTimestamp(): int
public getTimezone(): DateTimeZone|false
public __serialize(): array
public __unserialize(array `$data`): void
#[\Deprecated]
public __wakeup(): void
}

## Predefined Constants

`DateTimeInterface::ATOM` string
`DATE_ATOM`
  Atom (example: 2005-08-15T15:52:01+00:00); compatible with ISO-8601, RFC 3339, and XML Schema
`DateTimeInterface::COOKIE` string
`DATE_COOKIE`
  HTTP Cookies (example: Monday, 15-Aug-2005 15:52:01 UTC)
`DateTimeInterface::ISO8601` string
`DATE_ISO8601`
  ISO-8601-like (example: 2005-08-15T15:52:01+0000)

  > Note: This format is not compatible with ISO-8601, but is left this way for backward compatibility reasons. Use `DateTimeInterface::ISO8601_EXPANDED`, `DateTimeInterface::ATOM` for compatibility with ISO-8601 instead. (ref ISO8601:2004 section 4.3.3 clause d)

`DateTimeInterface::ISO8601_EXPANDED` string
`DATE_ISO8601_EXPANDED`
  ISO-8601 Expanded (example: +10191-07-26T08:59:52+01:00)

  > Note: This format allows for year ranges outside of ISO-8601's normal range of `0000`-`9999` by always including a sign character. It also ensures that the timezone part (`+01:00`) is compatible with ISO-8601.

`DateTimeInterface::RFC822` string
`DATE_RFC822`
  RFC 822 (example: Mon, 15 Aug 05 15:52:01 +0000)
`DateTimeInterface::RFC850` string
`DATE_RFC850`
  RFC 850 (example: Monday, 15-Aug-05 15:52:01 UTC)
`DateTimeInterface::RFC1036` string
`DATE_RFC1036`
  RFC 1036 (example: Mon, 15 Aug 05 15:52:01 +0000)
`DateTimeInterface::RFC1123` string
`DATE_RFC1123`
  RFC 1123 (example: Mon, 15 Aug 2005 15:52:01 +0000)
`DateTimeInterface::RFC7231` string
`DATE_RFC7231`
  RFC 7231 (since PHP 7.0.19 and 7.1.5) (example: Sat, 30 Apr 2016 17:52:13 GMT)
`DateTimeInterface::RFC2822` string
`DATE_RFC2822`
  RFC 2822 (example: Mon, 15 Aug 2005 15:52:01 +0000)
`DateTimeInterface::RFC3339` string
`DATE_RFC3339`
  Same as `DATE_ATOM`
`DateTimeInterface::RFC3339_EXTENDED` string
`DATE_RFC3339_EXTENDED`
  RFC 3339 EXTENDED format (example: 2005-08-15T15:52:01.000+00:00)
`DateTimeInterface::RSS` string
`DATE_RSS`
  RSS (example: Mon, 15 Aug 2005 15:52:01 +0000)
`DateTimeInterface::W3C` string
`DATE_W3C`
  World Wide Web Consortium (example: 2005-08-15T15:52:01+00:00)

## Changelog

Version | Description
--- | ---
8.5.0 | The `DATE_RFC7231` and `DateTimeInterface::RFC7231` constants have been deprecated.
8.4.0 | The class constants are now typed.
8.2.0 | The constant `DateTimeInterface::ISO8601_EXPANDED` was added.
7.2.0 | The class constants of DateTime are now defined on DateTimeInterface.

## Table of Contents

- DateTimeInterface::diff — Returns the difference between two DateTime objects
- DateTimeInterface::format — Returns date formatted according to given format
- DateTimeInterface::getOffset — Returns the timezone offset
- DateTimeInterface::getTimestamp — Gets the Unix timestamp
- DateTimeInterface::getTimezone — Return time zone relative to given DateTime
- DateTime::__serialize — Serialize a DateTime
- DateTime::__unserialize — Unserialize an Datetime
- DateTime::__wakeup — The __wakeup handler

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