scope_guard.h

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#ifndef SCOPE_GUARD_H
#define SCOPE_GUARD_H
 
/**
  @brief A Lambda to be called at scope exit.
 
  Used as std::scope_exit of sorts.
  Useful if you can't use unique_ptr to install a
  specific deleter but still want to do automatic
  cleanup at scope exit.
 
  @note Always use @ref create_scope_guard() instead of this template directly!
 
  Typical use is:
  @code
     ...
     foo_init();
     auto cleanup_foo = create_scope_guard([&] {
        foo_deinit();
     }
     ...
     if (some_error)
       return; // cleanup_foo calls foo_deinit()
     ...
     // foo_deinit is not going to be called past this point
     cleanup_foo.release();
     return; // return with foo initialized.
     ...
   @endcode
*/
template <typename TLambda>
class Scope_guard {
 public:
  Scope_guard(const TLambda &cleanup_lambda)
      : m_is_released(false), m_cleanup_lambda(cleanup_lambda) {}
  Scope_guard(const Scope_guard<TLambda> &) = delete;
  Scope_guard(Scope_guard<TLambda> &&moved)
      : m_is_released(moved.m_is_released),
        m_cleanup_lambda(moved.m_cleanup_lambda) {
    /* Set moved guard to "invalid" state, the one in which the cleanup lambda
      will not be executed. */
    moved.m_is_released = true;
  }
  ~Scope_guard() {
    if (!m_is_released) {
      m_cleanup_lambda();
    }
  }
 
  /**
    @brief Releases the scope guard
 
    Makes sure that when scope guard goes out of scope the
    cleanup lambda is not going to be called.
  */
  inline void release() { m_is_released = true; }
 
  /**
    @brief Calls the cleanup lambda and releases the scope guard
 
    Useful if you want to explicitly provoke the cleanup earlier
    than when going out of scope.
  */
  inline void reset() {
    if (!m_is_released) {
      m_cleanup_lambda();
      m_is_released = true;
    }
  }
 
 private:
  /** If true the cleanup is not going to be called */
  bool m_is_released;
  /** The cleanup to be called */
  const TLambda m_cleanup_lambda;
};
 
/**
  @brief Create a scope guard object
 
  Always use this instead of the @ref Scope_guard template itself!
  @sa @ref Scope_guard
 
  @tparam TLambda The type of the lambda. Inferred, never specify it.
  @param rollback_lambda The lambda to execute.
  @return Scope_guard<TLambda> An specialization of the @ref Scope_guard
  template.
*/
template <typename TLambda>
Scope_guard<TLambda> create_scope_guard(const TLambda rollback_lambda) {
  return Scope_guard<TLambda>(rollback_lambda);
}
 
/**
  Template class to scope guard variables.
*/
template <typename T>
class Variable_scope_guard {
 public:
  Variable_scope_guard() = delete;
  Variable_scope_guard(T &var) : m_var_ref(var), m_var_val(var) {}
 
  Variable_scope_guard(const Variable_scope_guard &) = delete;
  Variable_scope_guard(Variable_scope_guard &&) = delete;
 
  Variable_scope_guard &operator=(const Variable_scope_guard &) = delete;
  Variable_scope_guard &operator=(Variable_scope_guard &&) = delete;
 
  ~Variable_scope_guard() { m_var_ref = m_var_val; }
 
 private:
  T &m_var_ref;
  T m_var_val;
};
#endif /* SCOPE_GUARD_H */