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https://issues.apache.org/jira/browse/AVRO-3984?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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ASF GitHub Bot updated AVRO-3984:
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Labels: pull-request-available (was: )
> Improve generated code for unions (avrogencpp)
> ----------------------------------------------
>
> Key: AVRO-3984
> URL: https://issues.apache.org/jira/browse/AVRO-3984
> Project: Apache Avro
> Issue Type: Improvement
> Components: c++
> Reporter: Hagen Weiße
> Priority: Major
> Labels: pull-request-available
> Time Spent: 10m
> Remaining Estimate: 0h
>
> There are some issues in the code generated by avrogencpp for union types.
> The issues i would like to address in this ticket are listed below
> I will try to provide a pull request in the near future.
> h2. Performance
> h3. Setter
> The generated setter for a field takes a const reference and performs a copy
> for each set:
> {code:java}
> void set_BranchA(const BranchA& v); {code}
> This leads to redundant copies and performance issues if BranchA contains a
> large string or vector.
> A improvemnt could be to provide an additional setter with move semantics:
> {code:java}
> void set_BranchA(BranchA&& v); {code}
> h2. Getter
> The generated setter for a field returns a value:
> {code:java}
> BranchA get_BranchA() const;
> {code}
> This leads to a copy of BranchA, which might be a issue if BranchA is large
> or contains a large string/vector.
> It would propably be better to provide a reference to the stored value like
> this:
> {code:java}
> const BranchA& get_BranchA() const;
> BranchA& get_BranchA();
> {code}
> h2. std::any
> Generated unions store the value in a private std::any. This could probably
> be replaced with a std::variant which should prevent unnecessary heap
> allocations.
> h1. API issues
> h2. accessing union branches
> There are currently two ways to read a union branch:
> First using a get_[BRANCH] method. This will either return the value from the
> branch or throw an exception. This version is okay, if you know that this
> branch is set.
> Alternative is to use the idx() function. This will return a size_t with the
> index that is used.
> !https://ticket.rsint.net/images/icons/emoticons/warning.png|width=16,height=16!
> The issue here is that you need to manually implement a mapping between
> branch index -> union branch.
> A solution may look like this:
> {code:java}
> struct _Example_no_alias_avsc_Union__209__ {
> private:
> size_t idx_;
> std::any value_;
> public:
> enum class Index: size_t {
> BranchA = 0,
> BranchB = 1,
> BranchC = 2,
> };
> size_t idx() const { return idx_; }
> Index idx_enum() const { return static_cast<Index>(idx_); }
> bool is_BranchA() const;
> const AttributeGroup& get_BranchA() const;
> void set_BranchA(const BranchA& v);
> {code}
> Added stuff:
> * a enum with all union branches
> * a additional idx_enum() function that returns this Index enum
> * a is_[BRANCH] method, to check if a branch is set
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