Clash Royale CLAN TAG#URR8PPP

Execute the datetime command received as a string

I have date information "20.days.from_now" in a string format. With this datum, I should be able to find the exact date at any given point in time. But I couldn't find a way to execute it.

"20.days.from_now"

Tried:

1. "20.days.from_now".to_datetime => returns DateTime.now.beginning_of_day + 20.seconds
2. "20.days.from_now".to_datetime => returns Time.now.beginning_of_day + 20.seconds


Can't pass this as an argument to the Time/DateTime methods.

Time

DateTime

Is there an efficient way to achieve this?

Possible inputs could be:

1. "20.days.from_now"
2. "45.seconds.from_now"
3. "-11.months.from_now"
4. "3.years.from_now"
5. "15.hours.from_now"
6. "860.minutes.from_now"


3 Answers
3

No, Rails has no built-in way to do this (short of eval, which you definitely don't want).

eval

You'll need to write a parser, probably using regular expressions, specific for your use case.

Try something like:

ALLOWED_UNITS = %w(years months days hours minutes seconds)

if str =~ /A(-?d+).(w+).from_nowz/ and
ALLOWED_UNITS.include?($2)
$1.to_i.public_send($2).from_now
end


I agree with @matthewd. You could use eval but please don't.

eval

I would not use regex though.

Just split string and process it:

parts = input.split('.')
# assuming first part is always a number
number = parts[0].to_i
# what methods you allow user to chain
allowed_methods = %w[days seconds ...]
method_chain = parts[1..-1]
raise 'forbidden' unless method_chain.all?
# just invoke methods one by one
res = method_chain.reduce(number) r, m


Processing fully depends on what your input is expected to be

You first want to parse a number then its unit. You could achieve it by:

def parse_date_from_string(str)
number = str.split(".")[0].to_i
unit = str.split(".")[1]
return number.send(unit).from_now
end


Given your suggested inputs, the outputs would be:

[21] pry(main)> parse_date_from_string("20.days.from_now")
=> Sat, 01 Sep 2018 17:40:19 -03 -03:00
[22] pry(main)> parse_date_from_string("45.seconds.from_now")
=> Sun, 12 Aug 2018 17:41:04 -03 -03:00
[23] pry(main)> parse_date_from_string("-11.months.from_now")
=> Tue, 12 Sep 2017 17:40:19 -03 -03:00
[24] pry(main)> parse_date_from_string("3.years.from_now")
=> Thu, 12 Aug 2021 17:40:19 -03 -03:00
[25] pry(main)> parse_date_from_string("15.hours.from_now")
=> Mon, 13 Aug 2018 08:40:19 -03 -03:00
[26] pry(main)> parse_date_from_string("860.minutes.from_now")
=> Mon, 13 Aug 2018 08:00:19 -03 -03:00


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