How to use dynamic string substitution in Kotlin? - kotlin

Question

I'm looking for a Kotlin way to do a dynamic values substitution into a string.
It is clear how to implement it, just want to check if there is something similar in standard library.
Could you help me to find a function which given template and data map returns a resulting string with all template keys replaced with their values?
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

Not shorter than lukas.j's answer, just different (using Regex):
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

I did not find any thing standard to solve the problem.
So here is a balanced (readability/performance/extensibility) solution also handling cases when some substitutions are undefined in dataMap.
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
}
}