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Posted to issues@nifi.apache.org by GitBox <gi...@apache.org> on 2020/09/18 08:21:32 UTC

[GitHub] [nifi-minifi-cpp] hunyadi-dev opened a new pull request #911: MINIFICPP-1373 - Add proper FlowFile::getAttribute getter [QoL][mini-PR]

hunyadi-dev opened a new pull request #911:
URL: https://github.com/apache/nifi-minifi-cpp/pull/911


   Simple change extracted as separate commit, so that further changes will be easier to review.


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[GitHub] [nifi-minifi-cpp] hunyadi-dev commented on a change in pull request #911: MINIFICPP-1373 - Add proper FlowFile::getAttribute getter [QoL][mini-PR]

Posted by GitBox <gi...@apache.org>.
hunyadi-dev commented on a change in pull request #911:
URL: https://github.com/apache/nifi-minifi-cpp/pull/911#discussion_r542421625



##########
File path: libminifi/include/core/FlowFile.h
##########
@@ -129,7 +130,9 @@ class FlowFile : public core::Connectable, public ReferenceContainer {
    * @param value value to set
    * @return result of finding key
    */
-  bool getAttribute(std::string key, std::string& value) const;
+  bool getAttribute(const std::string& key, std::string& value) const;
+
+  utils::optional<std::reference_wrapper<const std::string>> getAttribute(const std::string& key) const;

Review comment:
       I am not arguing for safety, to plut it blunt I just do not like unnecessary copies.




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[GitHub] [nifi-minifi-cpp] hunyadi-dev closed pull request #911: MINIFICPP-1373 - Add proper FlowFile::getAttribute getter [QoL][mini-PR]

Posted by GitBox <gi...@apache.org>.
hunyadi-dev closed pull request #911:
URL: https://github.com/apache/nifi-minifi-cpp/pull/911


   


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[GitHub] [nifi-minifi-cpp] szaszm commented on a change in pull request #911: MINIFICPP-1373 - Add proper FlowFile::getAttribute getter [QoL][mini-PR]

Posted by GitBox <gi...@apache.org>.
szaszm commented on a change in pull request #911:
URL: https://github.com/apache/nifi-minifi-cpp/pull/911#discussion_r542328156



##########
File path: libminifi/include/core/FlowFile.h
##########
@@ -129,7 +130,9 @@ class FlowFile : public core::Connectable, public ReferenceContainer {
    * @param value value to set
    * @return result of finding key
    */
-  bool getAttribute(std::string key, std::string& value) const;
+  bool getAttribute(const std::string& key, std::string& value) const;
+
+  utils::optional<std::reference_wrapper<const std::string>> getAttribute(const std::string& key) const;

Review comment:
       Note: An optional of reference handlers should in general be replaced by a non-owning pointer. They have the same semantics, but tooling is better equipped to handle pointers.
   
   `auto` generally means safe value semantics, and it becoming a "serious misuse" is another footgun that reference types currently have to live with. How is this safer otherwise, than returning a const ref or non-owning pointer to const?
   
   (I'm continuing because I want to either convince you that this is better or understand your standpoint and why I'm wrong.)




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[GitHub] [nifi-minifi-cpp] szaszm commented on a change in pull request #911: MINIFICPP-1373 - Add proper FlowFile::getAttribute getter [QoL][mini-PR]

Posted by GitBox <gi...@apache.org>.
szaszm commented on a change in pull request #911:
URL: https://github.com/apache/nifi-minifi-cpp/pull/911#discussion_r490898307



##########
File path: libminifi/include/core/FlowFile.h
##########
@@ -129,7 +130,9 @@ class FlowFile : public core::Connectable, public ReferenceContainer {
    * @param value value to set
    * @return result of finding key
    */
-  bool getAttribute(std::string key, std::string& value) const;
+  bool getAttribute(const std::string& key, std::string& value) const;
+
+  utils::optional<std::reference_wrapper<const std::string>> getAttribute(const std::string& key) const;

Review comment:
       Why reference wrapper? I would avoid returning a reference to some internal data by default because of possible lifetime issues. If there is a certain need for this, I would call the function something else, like `getAttributeRef`.




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[GitHub] [nifi-minifi-cpp] arpadboda commented on a change in pull request #911: MINIFICPP-1373 - Add proper FlowFile::getAttribute getter [QoL][mini-PR]

Posted by GitBox <gi...@apache.org>.
arpadboda commented on a change in pull request #911:
URL: https://github.com/apache/nifi-minifi-cpp/pull/911#discussion_r540307778



##########
File path: libminifi/include/core/FlowFile.h
##########
@@ -129,7 +130,9 @@ class FlowFile : public core::Connectable, public ReferenceContainer {
    * @param value value to set
    * @return result of finding key
    */
-  bool getAttribute(std::string key, std::string& value) const;
+  bool getAttribute(const std::string& key, std::string& value) const;
+
+  utils::optional<std::reference_wrapper<const std::string>> getAttribute(const std::string& key) const;

Review comment:
       +1. 
   
   Moreover I also think that copying a string is not going to be the bottleneck in this software, so for safety reasons I would simply make it a copy. 




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[GitHub] [nifi-minifi-cpp] hunyadi-dev closed pull request #911: MINIFICPP-1373 - Add proper FlowFile::getAttribute getter [QoL][mini-PR]

Posted by GitBox <gi...@apache.org>.
hunyadi-dev closed pull request #911:
URL: https://github.com/apache/nifi-minifi-cpp/pull/911


   


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[GitHub] [nifi-minifi-cpp] hunyadi-dev commented on a change in pull request #911: MINIFICPP-1373 - Add proper FlowFile::getAttribute getter [QoL][mini-PR]

Posted by GitBox <gi...@apache.org>.
hunyadi-dev commented on a change in pull request #911:
URL: https://github.com/apache/nifi-minifi-cpp/pull/911#discussion_r542227113



##########
File path: libminifi/include/core/FlowFile.h
##########
@@ -129,7 +130,9 @@ class FlowFile : public core::Connectable, public ReferenceContainer {
    * @param value value to set
    * @return result of finding key
    */
-  bool getAttribute(std::string key, std::string& value) const;
+  bool getAttribute(const std::string& key, std::string& value) const;
+
+  utils::optional<std::reference_wrapper<const std::string>> getAttribute(const std::string& key) const;

Review comment:
       One needs to call `.value().get()` or `->get()` on an optional of reference handlers. It indeed would be an issue if someone seriously misused `auto` for holding the return value, but otherwise this is even safer than returning a const ref.
   https://godbolt.org/z/jbhf3n
   
   Will change this to **return a copy**  :cry:




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