Ruby - 在一行中使用多个条件
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Ruby - Using multiple conditions on a single line
提问by Jeffrey Green
So, I'm running into this issue wherein I want to have three conditions be checked before the routine continues, but it keeps throwing up syntax errors saying it didn't expect the multiple conditions. Now, I know I've seen other people use lines such as:
所以，我遇到了这个问题，我想在例程继续之前检查三个条件，但它不断抛出语法错误，说它不希望有多个条件。现在，我知道我已经看到其他人使用诸如：
if x > 100 && x % 2 == 1
#Do something
end
But, for whatever reason, this line:
但是，无论出于何种原因，这一行：
if (letters.eql? letters.upcase && dash.eql? '-' && numbers.to_i.to_s.eql? numbers)
is throwing up tons of errors. Is it something to do with '.eql?' or is it something extraneous about Ruby that I haven't encountered yet?
正在抛出大量错误。它与'.eql'有关吗？还是我还没有遇到过的关于 Ruby 的一些无关紧要的东西？
Here's the rest of the code for reference:
剩下的代码供参考：
print "Enter license plate: ";
input = gets.strip;
if input.length == 8
letters = input[0,2];
dash = input[3];
numbers = input[4,7];
if (letters.eql? letters.upcase && dash.eql? '-' && numbers.to_i.to_s.eql? numbers)
puts "#{input} is a valid license plate."
else
print "All valid license plates are three (3) uppercase letters, followed by a dash (-), followed by four (4) digits";
end
else
print "All valid license plates are 8 characters long.";
end
Also, these are the errors:
此外，这些是错误：
LicensePlate.rb:7: syntax error, unexpected tSTRING_BEG, expecting ')'
...? letters.upcase && dash.eql? '-' && numbers.to_i.to_s.eql? ...
... ^
LicensePlate.rb:7: syntax error, unexpected tIDENTIFIER, expecting ')'
... numbers.to_i.to_s.eql? numbers)
...
回答by Rob Mulholand
Think you're just missing some parens - try this:
认为你只是缺少一些括号 - 试试这个：
if (letters.eql?(letters.upcase) && dash.eql?('-') && numbers.to_i.to_s.eql?(numbers))
if (letters.eql?(letters.upcase) && dash.eql?('-') && numbers.to_i.to_s.eql?(numbers))
回答by Ryan Rebo
This should do it:
这应该这样做：
if letters.eql?(letters.upcase) && dash.eql?('-') && numbers.to_i.to_s.eql?(numbers)
if letters.eql?(letters.upcase) && dash.eql?('-') && numbers.to_i.to_s.eql?(numbers)
You can still wrap the entire conditional in parenthesis if you would like, but with Ruby (unlike JavaScript), you don't need to.
如果您愿意，您仍然可以将整个条件用括号括起来，但是对于 Ruby（与 JavaScript 不同），您不需要这样做。
回答by Ohad Dahan
This also works:
这也有效：
letters.eql? letters.upcase and dash.eql? '-' and numbers.to_i.to_s.eql? numbers
I believe this is due to operator precedence since this also works:
我相信这是由于运算符优先级，因为这也有效：
(letters.eql? letters.upcase) && (dash.eql? '-') && (numbers.to_i.to_s.eql? numbers)
Ruby seem to try and evaluate your condition prematurely.
Ruby 似乎过早地尝试评估您的状况。
EDIT: Just saw that Lurker was mentioning precedence previously.
编辑：刚刚看到 Lurker 之前提到了优先级。
回答by Stefan
In addition to the other answers - consider using a regular expressionto check the format:
除了其他答案 - 考虑使用正则表达式来检查格式：
print "Enter license plate: "
input = gets.chomp
if input.length != 8
puts "All valid license plates are 8 characters long."
elsif input !~ /^[A-Z]{3}-\d{4}$/
print "All valid license plates are three (3) uppercase letters, followed by a dash (-), followed by four (4) digits"
else
puts "#{input} is a valid license plate."
end
