Ruby：@cars.each |car| 之间的区别对于@cars 中的汽车

发布于 2024-07-29 02:59:20 字数 249 浏览 3 评论 0原文

（抱歉这个新手问题。）在 Ruby 中，循环：

@cars.each do |car|

和

for car in @cars do

之间有什么区别？

效率是否存在差异，或者为什么我们需要两种（或更多）方式来表达同一件事？第二种方式对我来说似乎更优雅/自然，但我可能错过了一些关键的观察，为什么第一种方式可能是更好的选择。

原文

(Sorry for the newbie question.) In Ruby, what is the difference between the loops:

@cars.each do |car|

and

for car in @cars do

is there a difference in efficiency, or why do we need two (or more) ways to express the same thing? The second way seems more elegant/natural to me, but I may be missing some crucial observation, why the first may be the better choice.

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泡沫很甜 2024-08-05 02:59:20

更多人使用 @cars.each 表示法，因为它可以推广到其他方法（例如 #inject、#each_with_index、#map< /code> 等，以及非迭代器回调）。

for/in 主要只是#each 的语法糖。两者工作方式的主要区别在于变量作用域：

irb> @cars = %w{ ford chevy honda toyota }
#=> ["ford", "chevy", "honda", "toyota"]
irb> @cars.each { |car| puts car }
ford
chevy
honda
toyota
#=> ["ford", "chevy", "honda", "toyota"]
irb> car
NameError: undefined local variable or method `car` for #<Object:0x399770 @cars=["ford", "chevy", "honda", "toyota"]>
        from (irb):3
        from /usr/local/bin/irb:12:in `<main>`
irb> for car in @cars
     puts car.reverse
     end
drof
yvehc
adnoh
atoyot
#=> ["ford", "chevy", "honda", "toyota"]
irb> car
#=> "toyota"

for/in 随后将迭代器变量保留在作用域中，而 #each 则不然。

就我个人而言，我从不使用 ruby 的 for/in 语法。

More people use the @cars.each notation because that generalizes to other methods (like #inject, #each_with_index, #map, etc, as well as non-iterator callbacks).

for/in is mainly just syntactic sugar for #each. The main difference in how the two work is in variable scoping:

irb> @cars = %w{ ford chevy honda toyota }
#=> ["ford", "chevy", "honda", "toyota"]
irb> @cars.each { |car| puts car }
ford
chevy
honda
toyota
#=> ["ford", "chevy", "honda", "toyota"]
irb> car
NameError: undefined local variable or method `car` for #<Object:0x399770 @cars=["ford", "chevy", "honda", "toyota"]>
        from (irb):3
        from /usr/local/bin/irb:12:in `<main>`
irb> for car in @cars
     puts car.reverse
     end
drof
yvehc
adnoh
atoyot
#=> ["ford", "chevy", "honda", "toyota"]
irb> car
#=> "toyota"

for/in leaves the iterator variable in scope afterwards, while #each doesn't.

Personally, I never use ruby's for/in syntax.

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