How can this be achieved in Ruby? Can it be done without repeating the variable? Javascript:
b = a || 7 This assigns a if a is not 0 and 7 otherwise
One specific case is converting date.wday to 7 if it returns 0 (Sunday).
5 Answers
Just out of curiosity:
class Object def javascript_or?(other) (is_a?(FalseClass) || nil? || '' == self || 0 == self) ? nil : self end end and:
a = b.javascript_or?(7) answered Jun 22, 2016 at 17:01
Aleksei Matiushkin
121k12 gold badges109 silver badges174 bronze badges
5 Comments
Cary Swoveland
Readers: mudsie has gone off his medication.
Aleksei Matiushkin
Aye. It’s time to get my pills, thanks @CarySwoveland for the reminder! See ya all tomorrow.
victorf
Rubyist will to power
tadman
Could also
case self which might be faster than this chain of || operators.Aleksei Matiushkin
@tadman Yeah, I thought about it (though I doubt it could be any faster,) but I on purpose made this answer as cryptic as possible.
There are only two falsy values in Ruby: nil and false. So, if you really want this approach
a = b == 0 ? 7 : b is a plausible solution, because 0 can't be evaluated as false.
However, a better option for your need is cwday, and not wday. Then you don't need to make this comparison anymore, because it returns 1 for Monday, 2 for Tuesday, and finally 7 for Sunday, as you need.
date = Date.new(2016,19,6) # => Jun 19 2016, Sunday date.cwday # => 7 
3 Comments
victorf
@CarySwoveland it's because you already have a 5-digit reputation here, Cary (; I'm just hi-lighting the most important part.
Aleksei Matiushkin
Frankly, I have a 3 digits (and one decimal point, though,) but I don’t need the bold face either.
Aleksei Matiushkin
For the sake of entropy constancy I upvoted it to give 10 rep more :)
For the particular case of 0 and 7:
a = (b + 6) % 7 + 1 :)
answered Jun 22, 2016 at 16:51
Aleksei Matiushkin
121k12 gold badges109 silver badges174 bronze badges
You can use ternary operator:
date.wday == 0 ? 7 : date.wday 8 Comments
Aurimas
That I could figure out by myself, any better versions? I edited the question to be just Ruby, not Rails
Ruby does not treat 0 as nil/false. It is one of the things you have to get used to. A better way would be to add your custom method to the Date class. You can find an example here: stackoverflow.com/questions/12343555/…
hightempo
0 evaluating to true is just part of the language. It's intentional. See, for example: stackoverflow.com/a/10387572/6441528 . If you want an exception, you should do something like build a utility class that provides one. I personally wouldn't override Date, at least not if you're working collaboratively. It'll just confuse anyone who shares your code.
Cary Swoveland
While I would use
cwday, I think this is a close second. I have no idea why it was downvoted, unless it was by the OP, who found it insulting. |
What you're describing here is less of a logical problem and more of a mapping one:
WEEKDAY_MAP = Hash.new { |h,k| h[k] = k < 7 ? k : nil }.merge(0 => 7) This one re-writes 1..6 to be the same, but 0 becomes 7. All other values are nil.
Then you can use this to re-write your day indicies:
b = WEEKDAY_MAP[a] If at some point you want to tinker with the logic some more, that's also possible.
4 Comments
Aurimas
Nice, but doesn't it look a bit more complicated than
day || 7 ? :Dtadman
@Aurimas Since Ruby is extremely strict about what's false in a logical sense,
|| 7 is never going to happen so you may as well abandon that idea: The When in Rome principle applies here. If you're doing a mapping operation, express it as such. In other languages you can take advantage of zero being a false value so the simplest expression of your desire does vary considerably depending on constraints.Aleksei Matiushkin
In fact, this is the best answer here, hence it narrows down the fact this is a mapping issue.
[date.wday, 7].detect { i != 0 }cwday(instead ofwday) – it returns7(instead of0) if the date is a Sunday ;-)wdayor not?cwdaysolved my case.