add conversion members to result

toml/result.hpp

@@ -8,6 +8,19 @@
 namespace toml
 {
 
+#if __cplusplus >= 201703L
+
+template<typename F, typename ... Args>
+using return_type_of_t = std::invoke_result_t<F, Args...>;
+
+#else
+// result_of is deprecated after C++17
+template<typename F, typename ... Args>
+using return_type_of_t = typename std::result_of<F(Args...)>::type;
+
+#endif
+
+
 template<typename T>
 struct success
 {
@@ -390,6 +403,142 @@ struct result
     error_type const& as_err() const& noexcept {return this->fail.value;}
     error_type&&      as_err() &&     noexcept {return std::move(this->fail.value);}
 
+
+    // prerequisities
+    // F: T -> U
+    // retval: result<U, E>
+    template<typename F>
+    result<return_type_of_t<F, value_type&>, error_type>
+    map(F&& f) &
+    {
+        if(this->is_ok()){return ok(f(this->as_ok()));}
+        return err(this->as_err());
+    }
+    template<typename F>
+    result<return_type_of_t<F, value_type const&>, error_type>
+    map(F&& f) const&
+    {
+        if(this->is_ok()){return ok(f(this->as_ok()));}
+        return err(this->as_err());
+    }
+    template<typename F>
+    result<return_type_of_t<F, value_type &&>, error_type>
+    map(F&& f) &&
+    {
+        if(this->is_ok()){return ok(f(std::move(this->as_ok())));}
+        return err(std::move(this->as_err()));
+    }
+
+    // prerequisities
+    // F: E -> F
+    // retval: result<T, F>
+    template<typename F>
+    result<value_type, return_type_of_t<F, error_type&>>
+    map_err(F&& f) &
+    {
+        if(this->is_err()){return err(f(this->as_err()));}
+        return ok(this->as_ok());
+    }
+    template<typename F>
+    result<value_type, return_type_of_t<F, error_type const&>>
+    map_err(F&& f) const&
+    {
+        if(this->is_err()){return err(f(this->as_err()));}
+        return ok(this->as_ok());
+    }
+    template<typename F>
+    result<value_type, return_type_of_t<F, error_type&&>>
+    map_err(F&& f) &&
+    {
+        if(this->is_err()){return err(f(std::move(this->as_err())));}
+        return ok(std::move(this->as_ok()));
+    }
+
+    // prerequisities
+    // F: T -> U
+    // retval: U
+    template<typename F, typename U>
+    return_type_of_t<F, value_type&>
+    map_or_else(F&& f, U&& opt) &
+    {
+        if(this->is_err()){return std::forward<U>(opt);}
+        return f(this->as_ok());
+    }
+    template<typename F, typename U>
+    return_type_of_t<F, value_type const&>
+    map_or_else(F&& f, U&& opt) const&
+    {
+        if(this->is_err()){return std::forward<U>(opt);}
+        return f(this->as_ok());
+    }
+    template<typename F, typename U>
+    return_type_of_t<F, value_type&&>
+    map_or_else(F&& f, U&& opt) &&
+    {
+        if(this->is_err()){return std::forward<U>(opt);}
+        return f(std::move(this->as_ok()));
+    }
+
+    // prerequisities:
+    // F: func T -> U
+    // toml::err(error_type) should be convertible to U.
+    // normally, type U is another result<S, F> and E is convertible to F
+    template<typename F>
+    return_type_of_t<F, value_type&>
+    and_then(F&& f) &
+    {
+        if(this->is_ok()){return f(this->as_ok());}
+        return err(this->as_err());
+    }
+    template<typename F>
+    return_type_of_t<F, value_type const&>
+    and_then(F&& f) const&
+    {
+        if(this->is_ok()){return f(this->as_ok());}
+        return err(this->as_err());
+    }
+    template<typename F>
+    return_type_of_t<F, value_type&&>
+    and_then(F&& f) &&
+    {
+        if(this->is_ok()){return f(std::move(this->as_ok()));}
+        return err(std::move(this->as_err()));
+    }
+
+    // prerequisities:
+    // F: func E -> U
+    // toml::ok(value_type) should be convertible to U.
+    // normally, type U is another result<S, F> and T is convertible to S
+    template<typename F>
+    return_type_of_t<F, error_type&>
+    or_else(F&& f) &
+    {
+        if(this->is_err()){return f(this->as_err());}
+        return ok(this->as_ok());
+    }
+    template<typename F>
+    return_type_of_t<F, error_type const&>
+    or_else(F&& f) const&
+    {
+        if(this->is_err()){return f(this->as_err());}
+        return ok(this->as_ok());
+    }
+    template<typename F>
+    return_type_of_t<F, error_type&&>
+    or_else(F&& f) &&
+    {
+        if(this->is_err()){return f(std::move(this->as_err()));}
+        return ok(std::move(this->as_ok()));
+    }
+
+    void swap(result<T, E>& other)
+    {
+        result<T, E> tmp(std::move(*this));
+        *this = std::move(other);
+        other = std::move(tmp);
+        return ;
+    }
+
   private:
 
     void cleanup() noexcept
@@ -409,6 +558,12 @@ struct result
     };
 };
 
+template<typename T, typename E>
+void swap(result<T, E>& lhs, result<T, E>& rhs)
+{
+    lhs.swap(rhs);
+    return;
+}
 
 } // toml11
 #endif// TOML11_RESULT_H