opwvhk commented on a change in pull request #1411:
URL: https://github.com/apache/avro/pull/1411#discussion_r755269337
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File path: doc/src/content/xdocs/idl.xml
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@@ -301,17 +301,32 @@ record Card {
<section id="unions">
<title>Unions</title>
<p>Union types are denoted as <code>union { typeA, typeB, typeC, ...
}</code>. For example,
- this record contains a string field that is optional (unioned with
<code>null</code>):
+ this record contains a string field that is optional (unioned with
<code>null</code>), and
+ a field containing either a precise or a imprecise number:
</p>
<source>
record RecordWithUnion {
union { null, string } optionalString;
+ union { decimal(12, 6), float } number;
}
</source>
<p>
Note that the same restrictions apply to Avro IDL unions as apply
to unions defined in the
- JSON format; namely, a record may not contain multiple elements of
the same type.
+ JSON format; namely, a record may not contain multiple elements of
the same type. Also,
+ fields/parameters that use the union type and have a default
parameter must specify a
+ default value of the same type as the <em>first</em>em> union type.
</p>
+ <p>Because it occurs so often, there is a special shorthand to
denote a union of
+ <code>null</code> with another type. The following two fields have
identical types:
+ </p>
+ <source>
+record RecordWithUnion {
+ union { null, string } optionalString1;
+ string? optionalString2;
+}
+ </source>
+ <p>Note that the union contains the <code>null</code> type first, so
the only allowed default
+ value is <code>null</code>.</p>
Review comment:
This documents the addition
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