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Message-ID: <BFDC5ABE-3155-4C4D-84DE-0FB1D9B37D32@9dev.de>
Date: Wed, 3 Mar 2021 11:37:42 +0100
To: internals@lists.php.net
Subject: Add __toString() to DateInterval
From: m@9dev.de (Moritz Friedrich)

Hi internals,
I=E2=80=99ve been active in the PHP ecosystem as @Radiergummi for quite =
a while now, but not on internals yet, so: nice to meet you all!

I would like to propose adding a `__toString()` method to the =
`DateInterval` class that should return a valid ISO8601 interval =
(https://en.wikipedia.org/wiki/ISO_8601#Time_intervals). As it stands, =
the class supports creating instances from such interval strings passed =
to its constructor, but the reverse isn=E2=80=99t true: The only way to =
build a string representation of the interval is by querying the =
`DateInterval::format` method for the individual durations multiple =
times (see =
https://stackoverflow.com/questions/33787039/format-dateinterval-as-iso860=
1#answers for examples).

Allowing to cast `DateInterval`s to strings would make the most sense in =
my opinion, and probably doesn=E2=80=99t break BC. Use cases include =
communicating with other APIs that work with ISO8601, or persistence of =
periods in databases, for example.=20

So instead of the following:

    function formatDateInterval(DateInterval $interval, string $default =
=3D 'PT0S'): string {
        return rtrim(str_replace(
            ['M0S', 'H0M', 'DT0H', 'M0D', 'P0Y', 'Y0M', 'P0M'],
            ['M', 'H', 'DT', 'M', 'P', 'Y', 'P'],
            $interval->format('P%yY%mM%dDT%hH%iM%sS')
        ), 'PT') ?: $default;
    }
   =20
    formatDateInterval(new DateInterval('P1DT5H')) =3D=3D=3D 'P1DT5H'

I=E2=80=99d like to be able to do this:

    (string)new DateInterval('P1DT5H') =3D=3D=3D 'P1DT5H'

Following alternative approaches come to mind:

1. Adding a new, specialized method to the class (eg. =
`DateInterval::toIsoString(): string`): =20
   While being the most BC-safe option, this would be completely =
different to the rest of the PHP date APIs.

2. Adding a new interval format constant to be passed to =
`DateInterval::format` (eg. `DATE_INTERVAL_ISO8601`): =20
   Most in line with the `DateTime` API, but probably requires special =
case handling in `format` code.

=46rom those, having `__toString` seems most desirable to me. =20
While I=E2=80=99m not proficient with C, I=E2=80=99d really like to see =
this implemented and would gladly help out where I can. Might someone be =
able to advise?


Sincerely
Moritz / Radiergummi=