ExtractCamelSnake

extractCamelSnakeConstant("HelloWorld")

## [1] "Hello" "World"

extractCamelSnakeConstant("helloWorld")

## [1] "hello" "World"

extractCamelSnakeConstant("hello_world")

## [1] "hello" "world"

extractCamelSnakeConstant("ZERO_FLAG")

## [1] "ZERO" "FLAG"

extractCamelSnakeConstant("UPPER_DELIMITER_CASE")

## [1] "UPPER"     "DELIMITER" "CASE"

#include <Rcpp.h>
#include <string>
using namespace Rcpp;

// [[Rcpp::plugins(cpp14)]]

bool isBreak(const char& ch) {
    if ('A' <= ch && ch <= 'Z') {
        return true;
    } else if (ch == '_') {
        return true;
    }
    return false;
}

bool isConstant(const std::string& words) {
    bool ret = true;
    for(auto& ch : words) {
        ret = ret && isBreak(ch);
        if (!ret)
            return ret;
    }
    return ret;
}

StringVector extractSnake(const std::string& words) {
    StringVector ret;
    std::string holder = "";
    for(auto& ch : words) {
        if (ch == '_') {
            if (holder.size() > 0) {
                ret.push_back(holder);
                holder = "";
            }
            if (ch != '_')
                holder += ch;
        } else {
            holder += ch;
        }
    }
    if (holder.size() > 0) {
        ret.push_back(holder);
    }
    return ret;
}

StringVector extractCamelSnake(const std::string& words) {
    StringVector ret;
    std::string holder = "";
    for(auto& ch : words) {
        if (isBreak(ch)) {
            if (holder.size() > 0) {
                ret.push_back(holder);
                holder = "";
            }
            if (ch != '_')
                holder += ch;
        } else {
            holder += ch;
        }
    }
    if (holder.size() > 0) {
        ret.push_back(holder);
    }
    return ret;
}

// [[Rcpp::export]]
StringVector extractCamelSnakeConstant(const std::string& words) {
    if (isConstant(words))
        return extractSnake(words);
    return extractCamelSnake(words);
}