ruby - 这是什么意思？

Question

例如《Why's Poignant Guide》中的以下代码:

def wipe_mutterings_from( sentence ) 
     unless sentence.respond_to? :include?
         raise ArgumentError, "cannot wipe mutterings from a #{ sentence.class }"
     end
     while sentence.include? '('
         open = sentence.index( '(' )
         close = sentence.index( ')', open )
         sentence[open..close] = '' if close
     end
end

Answer 1

在 Ruby 双引号字符串中——包括像 s = "…" 这样的字符串文字和 s = %Q{ ... }和 s = <<ENDCODE —语法#{ … }用于“字符串插值”，将动态内容插入到字符串中。例如:

i = 42
s = "I have #{ i } cats!"
#=> "I have 42 cats!"

它等同于(但更方便和效率)使用字符串连接以及显式调用to_s :

i = 42
s= "I have " + i.to_s + " cats!"
#=> "I have 42 cats!"

您可以在区域内放置任意代码，包括多行的多个表达式。评估代码的最终结果有to_s调用它以确保它是一个字符串值:

"I've seen #{
  i = 10
  5.times{ i+=1 }
  i*2
} weasels in my life"
#=> "I've seen 30 weasels in my life"

[4,3,2,1,"no"].each do |legs|
  puts "The frog has #{legs} leg#{:s if legs!=1}"
end
#=> The frog has 4 legs
#=> The frog has 3 legs
#=> The frog has 2 legs
#=> The frog has 1 leg
#=> The frog has no legs

---

请注意，这在单引号字符串中无效:

s = "The answer is #{6*7}" #=> "The answer is 42"
s = 'The answer is #{6*7}' #=> "The answer is #{6*7}"

s = %Q[The answer is #{ 6*7 }] #=> "The answer is 42"
s = %q[The answer is #{ 6*7 }] #=> "The answer is #{6*7}"

s = <<ENDSTRING
The answer is #{6*7}
ENDSTRING
#=> "The answer is 42\n"

s = <<'ENDSTRING'
The answer is #{6*7}
ENDSTRING
#=> "The answer is #{6*7}\n"

---

为方便起见，{}如果您只想插入实例变量(@foo)、全局变量($foo)或类变量(@@foo)的值，则字符串插值字符是可选的:

@cats = 17
s1 = "There are #{@cats} cats" #=> "There are 17 cats"
s2 = "There are #@cats cats"   #=> "There are 17 cats"