ruby 我可以在 `elsif` 上使用 `else if` 吗？
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Can I use `else if` over `elsif`?
提问by PrimRock
- Is it safe to use
else ifoverelsif? - Is it better to use
elsifbecause it follows Ruby's typing convention? - Or is this a preference?
- 使用
else ifover安全elsif吗？ elsif因为它遵循 Ruby 的类型约定，所以使用更好吗？- 或者这是一种偏好？
This is a piece of code taken from a book. I added extra endkeywords and swapped elsifkeywords with else ifs.
这是摘自一本书的一段代码。我添加了额外的end关键字并elsif用else ifs交换了关键字。
def describe(inhabitant)
if inhabitant == "sophie"
puts 'gender: female'
puts 'height: 145'
else if inhabitant == "paul"
puts 'gender: male'
puts 'height: 145'
else if inhabitant == "dawn"
puts 'gender: female'
puts 'height: 170'
else if inhabitant == "brian"
puts 'gender: male'
puts 'height: 180'
else if
puts 'species: Trachemys scripta elegans'
puts 'height: 6'
end
end
end
end
end
end
This made me realize how ugly else ifis.
这让我意识到有多丑else if。
回答by Yu Hao
You can use else ifand it's safe. However note that this means extra endkeywords are needed.
您可以使用else if，而且很安全。但是请注意，这意味着需要额外的end关键字。
if n == 1
puts "foo"
elsif n == 2
puts "bar"
end
is logically the same as:
在逻辑上是一样的：
if n == 1
puts "foo"
else if n == 2
puts "bar"
end
end
or the equivalent:
或等价物：
if n == 1
puts "foo"
else
if n == 2
puts "bar"
end
end
回答by onebree
TL;DR- Replacing elsifwith else ifis alright for a conditional with only 2 paths. Remember to close the second ifconditional created with else if. It is best practice to have as few levels of conditionals as you can, making for a less-complex method. So err on the side of caution and use elsif.
TL; DR-更换elsif带else if是不行了只有2路径的条件。请记住关闭if使用else if. 最好的做法是使用尽可能少的条件级别，从而使方法不那么复杂。因此，请谨慎使用elsif.
Depending on how you plan to write your method, else ifmaywork. It is not a good habit to get into, however.
根据您计划如何编写方法，else if可能会起作用。然而，这不是一个好习惯。
Take the following example. There are only 2 conditions. The second condition looks similar to elsif, but is interpreted as the second chunk of code:
以下面的例子为例。只有2个条件。第二个条件看起来类似于elsif，但被解释为第二个代码块：
# What you may want to write
if true
puts 'true'
else if false
puts 'false'
end
# How Ruby requires it
if true
puts 'true'
else
if false # You may also do: puts 'false' if false
puts 'false'
end
end
The first block will search for another endto close the primary conditional. Take note, you can bypass the extra end with a single line ifstatement. (I only suggest this if the executed code can be written on a single line.)
第一个块将搜索另一个end来关闭主要条件。请注意，您可以使用单行if语句绕过额外的结尾。（如果执行的代码可以写在一行上，我只建议这样做。）
It is important to note that once you declare an else, you may have no other conditionals in the same tier as that else. Given the second example above, the second ifis nested under the else. If you were to call elseor elsifon the same tier as the initial else, the conditional will fail.
重要的是要注意，一旦声明了 an else，在同一层中就可能没有其他条件了else。鉴于上面的第二个示例，第二个if嵌套在else. 如果您要调用else或elsif与初始 相同的层else，则条件将失败。
Here is when you would not want to implement else if:
这是您不想实施的时候else if：
def describe(inhabitant)
if inhabitant == "sophie"
puts 'gender: female'
puts 'height: 145'
elsif inhabitant == "paul"
puts 'gender: male'
puts 'height: 145'
elsif inhabitant == "dawn"
puts 'gender: female'
puts 'height: 170'
elsif inhabitant == "brian"
puts 'gender: male'
puts 'height: 180'
else
puts 'species: Trachemys scripta elegans'
puts 'height: 6'
end
end
Notice that neither of the elsifstatements can be "converted" to else ifin a clean way.
请注意，这两个elsif语句都不能else if以干净的方式“转换”为。
UPDATE: Thanks to Stefan, you can still use else if, leading to a very nested method.
更新：感谢Stefan，您仍然可以使用else if，从而导致非常嵌套的方法。
回答by spickermann
I would prefer elsifover else if. But that is just my opinion and technically there is no difference.
我宁愿elsif超过else if。但这只是我的意见，技术上没有区别。
But I would suggest to use a caseblock instead of multiple elsifyour example:
但我建议使用一个case块而不是多个elsif你的例子：
def describe(inhabitant)
case inhabitant
when "sophie"
puts 'gender: female'
puts 'height: 145'
when "paul"
puts 'gender: male'
puts 'height: 145'
when "dawn"
puts 'gender: female'
puts 'height: 170'
when "brian"
puts 'gender: male'
puts 'height: 180'
else
puts 'species: Trachemys scripta elegans'
puts 'height: 6'
end
Or I would store that mapping in a hash:
或者我将该映射存储在哈希中：
PEOPLE = {
'sophie' => { :gender => :female, :height => 145 },
'paul' => { :gender => :male, :height => 145 },
# ...
}
def describe(inhabitant)
description = PEOPLE.fetch(
inhabitant, { :species => 'Trachemys scripta elegans', :height => 6 }
)
puts "gender: #{description[:gender]}" if description[:gender]
puts "species: #{description[:species]}" if description[:species]
puts "height: #{description[:height]}"
end
回答by Wand Maker
You should pick the option that results in better readable code.I give below an example of code where I tend to feel that use of else ifis more readable.
您应该选择导致代码可读性更好的选项。我在下面给出了一个代码示例，我倾向于认为使用 的else if更具可读性。
result = "Unknown"
error_code = 911
# Version 1 - uses else if
if result == "Success"
puts "Good job!"
else
if error_code == "100"
puts "No worries, we can still recover"
else
puts "Hopeless case!"
end
end
# Version 2 - uses elsif
if result == "Success"
puts "Good job!"
elsif result != "Success" and error_code == "100"
puts "No worries, we can still recover"
else
puts "Hopeless case!"
end
My guess is this has to do something with Level of Abstraction. If all the conditions in the if-elsif-else-endare at same level, then it will be more readable. If they are at different levels, it may be beneficial to use fewelse ifin the code.
我的猜测是这与Level of Abstraction 有关系。如果 中的所有条件if-elsif-else-end都在同一级别，那么它会更具可读性。如果它们处于不同的级别，则else if在代码中少用一些可能会有好处。
