Extension methods in C++ using desperation, sweat, tears and bubblegum

extension_methods.cpp

#include <iostream>
#include <string>
#include <functional>

using namespace std::placeholders;

template<typename Signature>
struct Extension {
	std::function<Signature> func;

	template<typename Func>
	Extension(Func func) : func(func) {}
};

template<typename Signature>
void operator +(std::string& s, Extension<Signature> e) {
	e.func(s);
}

constexpr char whitespace[] = " \f\n\r\t\v";

Extension<void(std::string&)> trim() {
	return [](std::string& s) {
		auto start = s.find_first_not_of(whitespace);
		auto end = s.find_last_not_of(whitespace);

		if (start != std::string::npos) s.erase(0, start);
		if (end != std::string::npos) s.erase(end - start, s.size());
	};
}

Extension<void(std::string&)> append(char c) {
	return std::bind([](std::string& s, char c) {
		s += c;
	}, _1, c);
}

int main() {
	std::string s = "   Hello world! ";
	std::cout << '"' << s << "\"\n";
	s+trim();
	std::cout << '"' << s << "\"\n";
	s+append('x');
	std::cout << '"' << s << "\"\n";
	return 0;
}