ruby - 正则表达式的 o 修饰符是什么意思？

Question

Ruby 正则表达式有一些选项(例如 i、x、m、o)。例如，i 表示忽略大小写。

o 选项是什么意思？在 ri Regexp 中，它说 o 表示只执行一次 #{} 插值。但是当我这样做时:

a = 'one'  
b = /#{a}/  
a = 'two'  

b 不变(它保持为 /one/)。我错过了什么？

Answer 1

直接来自 the go-to source for regular expressions :

/o causes any #{...} substitutions in a particular regex literal to be performed just once, the first time it is evaluated. Otherwise, the substitutions will be performed every time the literal generates a Regexp object.

我也可以找到 this usage example :

# avoid interpolating patterns like this if the pattern
# isn't going to change:
pattern = ARGV.shift
ARGF.each do |line|
    print line if line =~ /#{pattern}/
end

# the above creates a new regex each iteration. Instead,
# use the /o modifier so the regex is compiled only once

pattern = ARGV.shift
ARGF.each do |line|
    print line if line =~ /#{pattern}/o
end

所以我想这对编译器来说更像是一件事情，因为单行会被多次执行。