tag stack with hash identifier

tag_stack.cc

#include <string>			// with std::hash<std::string>
#include <utility>			// for std::move

#include <sstream>
#include <vector>
#include <iomanip>			// for std::quoted


namespace tag_stack_detail
{
	struct tag_stack
	{
		void push(std::string const& x) { push_formatted(format(x)); }
		void pop() { stack.pop_back(); }
		auto& top() const { return stack.back(); }
		auto top_id() const { return hash(top()); }
		operator bool () const { return stack.size(); }

	private:
		std::vector<std::string> stack;
		std::hash<std::string> hash;

		void push_formatted(std::string x)
		{
			if (stack.size()) x = top() + x;
			stack.emplace_back(std::move(x));
		}

		static std::string format(std::string const& x)
		{
			std::ostringstream ss;
			ss << std::quoted(x, '/');
			auto s = ss.str();
			s.pop_back();
			return s;
		}
	};
}
using tag_stack_detail::tag_stack;


//-------------------------- testing ------------------------------
#include <iostream>
#include <functional>
using std::cerr;

namespace
{
	struct scope_guard
	{
		using destructor = std::function<void ()>;
		scope_guard(destructor dtor) : dtor{std::move(dtor)} {}
		~scope_guard() { dtor(); }
		auto cancel() { return std::move(dtor); }

		// only movable
		scope_guard(scope_guard &&) = default;
		scope_guard(scope_guard const&) = delete;
		scope_guard& operator = (scope_guard &&) = default;
		scope_guard& operator = (scope_guard const&) = delete;

	private:
		const destructor dtor;
	};

	void inspect(tag_stack const& ts)
	{
		constexpr auto pointer_size = sizeof(void*);
		cerr << std::setw(2*pointer_size) << std::setfill('0')
			<< std::hex << ts.top_id() << ": " << ts.top() << "\n";
	}

	scope_guard push(tag_stack& ts, std::string const& x)
	{
		ts.push(x);
		cerr << "push ";
		inspect(ts);
		return {[&ts] {
			cerr << "pop  ";
			inspect(ts);
			ts.pop();
		}};
	}

	auto push(tag_stack& ts, int x) { return push(ts, std::to_string(x)); }
}



int main()
{
	tag_stack ts;
	auto _1 = push(ts, R"tag(gar/ba\ge)tag");
	auto _2 = push(ts, R"tag(tree)tag");
	auto _3 = push(ts, R"tag(node)tag");
	for (int i=0; i<10; i++)
		push(ts, i);
}

zzzzzzzz-possible-output

push 3d90e898df906cc4: /gar\/ba\\ge
push fb3a3017c9f99f73: /gar\/ba\\ge/tree
push 19964e57ac82223e: /gar\/ba\\ge/tree/node
push 4fd535267d400fc6: /gar\/ba\\ge/tree/node/0
pop  4fd535267d400fc6: /gar\/ba\\ge/tree/node/0
push e10651048e5e484c: /gar\/ba\\ge/tree/node/1
pop  e10651048e5e484c: /gar\/ba\\ge/tree/node/1
push 0a46755946cb5c1a: /gar\/ba\\ge/tree/node/2
pop  0a46755946cb5c1a: /gar\/ba\\ge/tree/node/2
push 2036d911db5cf454: /gar\/ba\\ge/tree/node/3
pop  2036d911db5cf454: /gar\/ba\\ge/tree/node/3
push 1cf920d039696c48: /gar\/ba\\ge/tree/node/4
pop  1cf920d039696c48: /gar\/ba\\ge/tree/node/4
push 4b4a2f69ca0b9a5c: /gar\/ba\\ge/tree/node/5
pop  4b4a2f69ca0b9a5c: /gar\/ba\\ge/tree/node/5
push ee14365926808a2b: /gar\/ba\\ge/tree/node/6
pop  ee14365926808a2b: /gar\/ba\\ge/tree/node/6
push 44d58e7c66a68c24: /gar\/ba\\ge/tree/node/7
pop  44d58e7c66a68c24: /gar\/ba\\ge/tree/node/7
push 0a4981f430bf6ba2: /gar\/ba\\ge/tree/node/8
pop  0a4981f430bf6ba2: /gar\/ba\\ge/tree/node/8
push cf2375ead1618810: /gar\/ba\\ge/tree/node/9
pop  cf2375ead1618810: /gar\/ba\\ge/tree/node/9
pop  19964e57ac82223e: /gar\/ba\\ge/tree/node
pop  fb3a3017c9f99f73: /gar\/ba\\ge/tree
pop  3d90e898df906cc4: /gar\/ba\\ge