asserts.h

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#ifndef FCPP_VALIDATIONS_H
#define FCPP_VALIDATIONS_H
 
#include <sstream>
#include <string>
 
namespace fcpp::asserts {
 
class invariant {
private:
  const bool condition_;
  std::stringstream message_;
 
  invariant(bool condition, std::string message)
      : condition_(condition), message_(message) {}
 
  // https://herbsutter.com/2014/05/03/reader-qa-how-can-i-prevent-a-type-from-being-instantiated-on-the-stack/
  invariant() = delete;
  invariant(const invariant &) = default;
 
public:
  ~invariant() noexcept(false) {
    if (!condition_) {
      // Living dangerously, guaranteed not to live on the stack though. See
      // above link.
      throw std::invalid_argument(  // lgtm [cpp/throw-in-destructor]
          message_.str());
    }
  }
 
  template <typename Text>
  friend invariant &&operator<<(invariant &&item, const Text &text) {
    item.message_ << text;
    return std::move(item);
  }
 
  static invariant eval(bool condition) { return invariant(condition, ""); }
};
 
} // namespace fcpp::asserts
 
#endif // FCPP_VALIDATIONS_H