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https://issues.apache.org/jira/browse/AVRO-1750?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15244945#comment-15244945
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Ryan Blue commented on AVRO-1750:
---------------------------------
[~braden], could you take a look at the new patch?
> GenericDatum API behavior breaking change
> -----------------------------------------
>
> Key: AVRO-1750
> URL: https://issues.apache.org/jira/browse/AVRO-1750
> Project: Avro
> Issue Type: Bug
> Components: c++
> Affects Versions: 1.7.7
> Reporter: Braden McDaniel
> Assignee: Thiruvalluvan M. G.
> Fix For: 1.9.0
>
> Attachments: AVRO-1750.patch
>
>
> It appears that a change was introduced to the {{avro::GenericDatum}}
> implementation between 1.7.6 and 1.7.7 that causes unions to be handled
> differently.
> The 1.7.6 implementation does this:
> {noformat}
> inline Type AVRO_DECL GenericDatum::type() const {
> return (type_ == AVRO_UNION) ?
> boost::any_cast<GenericUnion>(&value_)->type() : type_;
> }
> template<typename T>
> const T& GenericDatum::value() const {
> return (type_ == AVRO_UNION) ?
> boost::any_cast<GenericUnion>(&value_)->value<T>() :
> *boost::any_cast<T>(&value_);
> }
> template<typename T>
> T& GenericDatum::value() {
> return (type_ == AVRO_UNION) ?
> boost::any_cast<GenericUnion>(&value_)->value<T>() :
> *boost::any_cast<T>(&value_);
> }
> {noformat}
> …whereas the 1.7.7 implementation does this:
> {noformat}
> /**
> * The avro data type this datum holds.
> */
> Type type() const {
> return type_;
> }
> /**
> * Returns the value held by this datum.
> * T The type for the value. This must correspond to the
> * avro type returned by type().
> */
> template<typename T> const T& value() const {
> return *boost::any_cast<T>(&value_);
> }
> /**
> * Returns the reference to the value held by this datum, which
> * can be used to change the contents. Please note that only
> * value can be changed, the data type of the value held cannot
> * be changed.
> *
> * T The type for the value. This must correspond to the
> * avro type returned by type().
> */
> template<typename T> T& value() {
> return *boost::any_cast<T>(&value_);
> }
> {noformat}
> The result of this is that, if the underlying value is an {{AVRO_UNION}},
> calls to {{GenericDatum::type}} and {{GenericDatum::value<>}} that previously
> resolved to the union member type no longer do so (and user code relying on
> that behavior has been broken).
> This change apparently was made as part of the changes for AVRO-1474;
> however, looking at the comments in that issue, it's not clear to me why it
> was required for that fix.
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