regex_replace

def measure(f: () => Unit) {
    val start = System.currentTimeMillis()
    f()
    println(s"Elapsed: ${System.currentTimeMillis()-start}ms")
}

val str = ". ? + * | { } [ ] ( ) \" \\ # @ & < > ~"

measure(() =>
    for { i <- 0 to 10000000 } {
        val escaped = str.replaceAll("""([\.\?\+\*\|\{\}\[\]\(\)\"\\\#\@\&\<\>\~])""", """\\\\$1""")
    }
)

val r = java.util.regex.Pattern.compile("""([\.\?\+\*\|\{\}\[\]\(\)\"\\\#\@\&\<\>\~])""")
measure(() =>
    for { i <- 0 to 10000000 } {
        val escaped = r.matcher(str).replaceAll("""\\\\$1""")
    }
)

measure(() =>
    for { i <- 0 to 10000000 } {
        val escaped = escape(str)
    }
)

def escape(str: String): String = {
    val chars = str.toCharArray()
    val sb = new StringBuffer(2 * chars.length)
    var i = 0
    while (i < str.length) {
        val c = chars(i)
        (c: @scala.annotation.switch) match {
            case '.' | '?' | '+' | '*' | '|' | '{' |
                 '}' | '[' | ']' | '(' | ')' | '"' |
                '\\' | '#' | '@' | '&' | '<' | '>' | '~' => sb.append("""\\\\""").append(c)
            case _ => sb.append(c)
        }
        i += 1
    }
    sb.toString()
}