如何在 Kotlin 中使用动态字符串替换？

Question

我正在寻找一种 Kotlin 方法来将动态值替换为字符串。实现方法已经很清楚了，就是想看看标准库里有没有类似的东西。

你能帮我找到一个给定 template 和 data 映射 returns 结果字符串的函数吗？

fun format(template: String, data: Map<String, Any>): String { /* magic */ }

format("${a} ${b} ${a}", mapOf("a" to "Home", "b" to "Sweet))   // -> "Home Sweet Home"

Answer 1

fun format(template: String, data: Map<String, String>): String {
  var retval = template
  data.forEach { dataEntry ->
    retval = retval.replace("${" + dataEntry.key + "}", dataEntry.value)
  }
  return retval
}

// The $ signs in the template string need to be escaped to prevent
// string interpolation
format("${a} ${b} ${a}", mapOf("a" to "Home", "b" to "Sweet"))

Answer 2

不比lukas.j的答案短，只是不同（使用正则表达式）：

val regex = "\$\{([a-z])}".toRegex()

fun format(template: String, data: Map<String, String>) =
    regex.findAll(template).fold(template) { result, matchResult ->
        val (match, key) = matchResult.groupValues
        result.replace(match, data[key] ?: match)
    }

Answer 3

我没有找到任何解决问题的标准。

所以这是一个平衡的 (readability/performance/extensibility) 解决方案，它还可以处理 dataMap 中未定义某些替换的情况。

makeString("${a} # ${b} @ ${c}", mapOf("a" to 123, "c" to "xyz"))   // => "123 # ??? @ xyz"

--

object Substitutions {
    private val pattern = Pattern.compile("\$\{([^}]+)\}")

    fun makeString(
        template: String, 
        dataMap: Map<String, Any?>, 
        undefinedStub: String = "???"
    ): String {
        val replacer = createReplacer(dataMap, undefinedStub)
        val messageParts = splitWithDelimiters(template, pattern, replacer)
        return messageParts.joinToString("")
    }

    private fun createReplacer(dataMap: Map<String, Any?>, stub: String): (Matcher) -> String {
        return { m ->
            val key = m.group(1)
            (dataMap[key] ?: stub).toString()
        }
    }

    private fun splitWithDelimiters(
        text: String,
        pattern: Pattern,
        matchTransform: (Matcher) -> String
    ): List<String> {
        var lastMatch = 0
        val items = mutableListOf<String>()
        val m = pattern.matcher(text)

        while (m.find()) {
            items.add(text.substring(lastMatch, m.start()))
            items.add(matchTransform(m))
            lastMatch = m.end()
        }

        items.add(text.substring(lastMatch))

        return items
    }
}

如何在 Kotlin 中使用动态字符串替换？

How to use dynamic string substitution in Kotlin?

string-substitution

kotlin