Description:
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---
From manual page: http://www.php.net/intldateformatter.format
---

As of PHP 7.1.5 IntlDateFormatter->format() accepts any DateTimeInterface object, not just DateTime.


Test script:
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<?php

$datetime = new DateTimeImmutable('2017-07-13');

$prettyDateFormatter = new IntlDateFormatter('en_US', IntlDateFormatter::FULL, IntlDateFormatter::FULL, 'America/Chicago', IntlDateFormatter::GREGORIAN, 'yyyy-MM-dd');
$prettyDateFormatter->setPattern('MMM d yyyy');

echo 'Timestamp: ', $prettyDateFormatter->format($datetime->getTimestamp()) ?: $prettyDateFormatter->getErrorMessage(), "\n";
echo 'DateTime: ', $prettyDateFormatter->format(new DateTime('2017-07-13')) ?: $prettyDateFormatter->getErrorMessage(), "\n";
echo 'DateTimeImmutable: ', $prettyDateFormatter->format($datetime) ?: $prettyDateFormatter->getErrorMessage(), "\n";


Expected result:
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PHP >= 7.1.5:
Timestamp: Jul 12 2017
DateTime: Jul 12 2017
DateTimeImmutable: Jul 12 2017

PHP < 7.1.5:
Timestamp: Jul 12 2017
DateTime: Jul 12 2017
DateTimeImmutable: datefmt_format: invalid object type for date/time (only IntlCalendar and DateTime permitted): U_ILLEGAL_ARGUMENT_ERROR

PHP >= 7.1.5 has changed signature to:
datefmt_format: invalid object type for date/time (only IntlCalendar and DateTimeInterface permitted): U_ILLEGAL_ARGUMENT_ERROR

Actual result:
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https://3v4l.org/0ErGG

Output for hhvm-3.18.4 - 3.21.0, 7.1.5 - 7.2.0beta2
Timestamp: Jul 12 2017
DateTime: Jul 12 2017
DateTimeImmutable: Jul 12 2017

Output for 5.6.0 - 5.6.30, 7.0.0 - 7.1.4
Timestamp: Jul 12 2017
DateTime: Jul 12 2017
DateTimeImmutable: datefmt_format: invalid object type for date/time (only IntlCalendar and DateTime permitted): U_ILLEGAL_ARGUMENT_ERROR