Test.cpp

#include <iostream>
#include <boost/xpressive/xpressive.hpp>

// --regex-kotlin=/^[ \t]*(private|protected|public)?[ \t]*((abstract|final|sealed)[ \t]*)*(data[ \t]*)?class[ \t]+([a-zA-Z0-9_]+)/\8/c,class/

namespace xp = boost::xpressive;

int main() {
    // 基本コンビネーター
    xp::sregex empty = xp::sregex::compile("");
    xp::sregex blank = *xp::space;
    // Converts a string to xp::sregex
    auto let = [empty](std::string x){
        return x >> empty;
    };

    // 目的たち
    xp::sregex visibility =
        (let("private") | "protected" | "public")
        >> blank
        ;

    xp::sregex kind =
        (let("abstract") | "final" | "sealed")
        >> blank
        ;

    xp::sregex class_ =
        blank
        >> !visibility
        >> !kind
        >> !let("data") >> blank
        >> "class" >> blank
        >> (xp::s1 = *(xp::alnum | '_'))
        >> *xp::_
        ;

    // Go!!
    xp::smatch what;
    std::string x = "public data class You(val me: String)";
    std::string y = "sealed class Product {}";

    if (xp::regex_match(x, what, class_)) {
        std::cout << what[0] << '\n';
    }
    if (xp::regex_match(y, what, class_)) {
        std::cout << what[0] << '\n';
    }
}