Rails: use Date.strptime to parse date

It is very common to parse dates from strings. It seems obvious to use Date.parse for this job. However this method does not validate the input and tries to guess the format of the string.

This can lead to a very unexpected results:

> Date.parse('Foobar_09_2018')
Tue, 09 Oct 2018

In most of the cases it would be better to use Date.strptime as you can provide a date or time pattern to match against.

> Date.strptime('Foobar_09_2018', '%d_%m_%Y')
ArgumentError (invalid strptime format - `%d_%m_%Y')
> Date.strptime('01_09_2018', '%d_%m_%Y')
Sat, 01 Sep 2018

other use cases:

ambiguous date strings

>> Date.parse('01.02.03')
=> Sat, 03 Feb 2001

In Germany you would expect this to be parsed as 01 Feb 2003.
Be more explicit and provide a date pattern:

>> Date.strptime('01.02.03', '%d.%m.%y')
=> Sat, 01 Feb 2003