Demonstrates strange behavior of std::optional

optional.cpp

#include <iostream>
#include <optional>
#include <string>

struct Delete {
	std::string str = "delete";
	Delete() = delete;
	Delete(const Delete &) = delete;
	Delete(Delete &&) = delete;
	Delete(const std::string &str_): str(str_) {
		std::cout << "Constructing Delete(\"" << str_ << "\")\n";
	}
};

struct Default {
	std::string str = "default";
	Default() {
		std::cout << "Constructing Default()\n";
	}
	Default(const Default &) = delete;
	Default(Default &&) = delete;
	Default(const std::string &str_): str(str_) {
		std::cout << "Constructing Default(\"" << str_ << "\")\n";
	}
};

int main() {
	std::optional<Delete> delete_opt;
	Delete &del = *delete_opt; // No error
	std::cout << "(" << del.str << ") @ " << &del << "\n"; // Empty

	std::optional<Default> default_opt;
	Default &def = *default_opt; // Silent
	std::cout << "(" << def.str << ") @ " << &def << "\n"; // Empty
}

Sample output for both clang++ and g++:

() @ 0x7ffee6942580
() @ 0x7ffee6942548