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To anyone who's wondering, it seems like 'and' and 'or' are the same as && and ||, but with lower precedence [0]. Does anyone have a good reason why they both e
by alanctgardner2 14y ago
To anyone who's wondering, it seems like 'and' and 'or' are the same as && and ||, but with lower precedence [0]. Does anyone have a good reason why they both exist? It's a pretty big gotcha.
[0] http://stackoverflow.com/questions/1426826/difference-between-and-and-in-ruby http://stackoverflow.com/questions/1426826/difference-betwee...
- philwelch 14y agoIt's an imported Perlism, back from the days of the old assert idiom `foo == bar or die`. If `foo == bar` evaluates to true, the `or` is short-circuited, else it calls the built-in `die` function which kills the process.
- lloeki 14y agoMore precisely && and || are meant to stand in boolean tests, whereas and and or are meant to tie expressions together DSL style, as an alternative to if/then, like so: @current_user.logged_in? or redirect_to login_path @current_user.can? :do_this or render :status => 403 shirt.blue? and return bar put_suit_on or put_pants_on
- graywh 14y agoThat's a good example shirt.blue? and return bar would be equivalent to return bar if shirt.blue? You can do the same with or and unless.
- philwelch 14y agoI find the postfix if and unless far more readable than the Perlish and and or operators. The "or die" construction for asserts is really amusing though.
- gurkendoktor 14y ago&&/|| can bite you just as well: if first_user = User.find(4) && second_user = User.find(6) ... end
- rauljara 14y agoI may be missing something obvious here. How would this code bite you?
- alanctgardner2 14y ago> first_user = User.find(4) && second_user = User.find(6) It looks like it would evaluate as: first_user = (User.find(4) and second_user = User.find(6)) That is to say, the assignment comes after the boolean operation, which is unexpected.
- pooriaazimi 14y agoWell, I expect first_user = User.find(4) && second_user = User.find(6) to be literally equivalent to second_user = User.find(6) first_user = User.find(4) && second_user I honestly can't see why you might want it to mean something else... Edit: I see. if you do something like if (first_user = User.find(4) && second_user = User.find(6)) { .. } it might bite you. You might expect it to be equivalent to first_user = User.find(4) second_user = User.find(6) if (first_user && second_user) { .. } which I personally think is a very, very bad practice. Parenthesis should always be used when there's even the slightest possibility that you or another maintainer/contributor might be confused about.
- alanctgardner2 14y agoPersonally, I'm almost painfully verbose with my parens to avoid exactly this scenario. Better to be explicit about my intent to the interpreter and other coders. Having an assignment that could be skipped by short-circuiting also seems like bad practice, but I realize it was designed to be a toy example