Ruby syntax: break out from 'each.. do..' block
I am developing a Ruby on Rails app. My question is more about Ruby syntax.
I have a model class with a class method self.check
:
class Cars < ActiveRecord::Base
...
def self.check(name)
self.all.each do |car|
#if result is true, break out from the each block, and return the car how to...
result = SOME_CONDITION_MEET?(car) #not related with database
end
puts "outside the each block."
end
end
I would like to stop/break out from the each
block once the result
is true (that's break the each
block if car.name
is the same as the name
parameter once) AND return the car
which cause the true result. How to break out in Ruby code?
You can break with the break
keyword. For example
[1,2,3].each do |i|
puts i
break
end
will output 1
. Or if you want to directly return the value, use return
.
Since you updated the question, here the code:
class Car < ActiveRecord::Base
# …
def self.check(name)
self.all.each do |car|
return car if some_condition_met?(car)
end
puts "outside the each block."
end
end
Though you can also use Array#detect
or Array#any?
for that purpose.
I provide a bad sample code. I am not directly find or check something from database. I just need a way to break out from the "each" block if some condition meets once and return that 'car' which cause the true result.
Then what you need is:
def check(cars, car_name)
cars.detect { |car| car.name == car_name }
end
If you wanted just to know if there was any car with that name then you'd use Enumerable#any?
. As a rule of thumb, use Enumerable#each
only to do side effects, not perform logic.
you can use include?
method.
def self.check(name)
cars.include? name
end
include?
returns true
if name
is present in the cars
array else it returns false
.
You can use break
but what your are trying to do could be done much easier, like this:
def self.check(name)
return false if self.find_by_name(name).nil?
return true
end
This uses the database. You are trying to use Ruby at a place the database can deal with it better.
You can also use break
conditional:
break if (car.name == name)
I had to do this exact same thing and I was drawing a blank. So despite this being a very old question, here's my answer:
Note: This answer assumes you don't want to return the item as it exists within the array, but instead do some processing on the item and return the result of that instead. That's how I originally read the question, I realise now that was incorrect - though this approach can be easily modified for that effect (break item
insead of break output
)
Since returning from blocks is dodgy (nobody likes it, and I think the rules are about to change which makes it even more fraught) this is a much nicer option:
collection.inject(nil) do |_acc, item|
output = expensive_operation(item)
break output if output
end
Note that there are lots of variants; for example, if you don't want an incidental variable, and don't mind starting a second loop in some circumstances, you can invert it like this:
collection.inject(nil) do |acc, item|
break acc if acc
expensive_operation(item)
end