Add union type design overview. #3119
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| static AttributeValue.Builder builder(); | ||
| static fromS(String s); | ||
| static fromN(String s); | ||
| static fromB(String s); |
| void accept(AttributeValue.VoidVisitor visitor); | ||
| <T> T accept(AttributeValue.Visitor<T> visitor); |
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I was wondering, should we have these? The customer can do a switch based on the type() for something equivalent.
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Conclusion from review: They might be nice, but the void visitor is basically just a switch on the type() and the visitor is just a switch expression on the type() (added in Java 17). Admittedly, not a lot of customers are on 17 right now, but it would be good not to add it if we can avoid it. We'll end up waiting for customer feedback on this one before we add it.
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| ## Union Type Definition | ||
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| We will follow the patterns set by `Document` and `JsonNode`, because the pattern used by `AudioStream` would not be backwards-compatible with existing types and does not function particularly well for union type members that are not structures. |
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Can you explain what the "...does not function particularly well for union type members that are not structures." means?
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| We currently implement friendly tagged unions in at least two external places within the SDK already: | ||
| 1. The `software.amazon.awssdk.core.document.Document` type. | ||
| 2. Event stream types, like TranscribeStreaming's `software.amazon.awssdk.services.transcribestreaming.model.AudioStream` type. |
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A better example (or in addition to) might be one of newer eventstreams like in Lex, which use the newer style of eventstream generation that supports 1:M of shapes to events
| **After Changes** | ||
| ```java | ||
| String result = attributeValue.visit(new AttributeValue.Visitor<String>(){ | ||
| String visitS(String s) { return s; } | ||
| String visitN(String n) { return n; } | ||
| String visitB(SdkBytes b) { return b.asUtf8String(); } | ||
| }); | ||
| ``` |
| ```java | ||
| attributeValue.visit(new AttributeValue.VoidVisitor() { | ||
| void visitS(String s) { System.out.println(s); } | ||
| void visitN(String n) { System.out.println(n); } | ||
| void visitB(SdkBytes b) { System.out.println(b.asUtf8String()); } |
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Or using pattern matching for switch!
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Service models marked as a union type have additional helper methods to take advantage of the knowledge that just one member is expected to be set. More information: #3119
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Kudos, SonarCloud Quality Gate passed!
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* Added support for modeling union types. Service models marked as a union type have additional helper methods to take advantage of the knowledge that just one member is expected to be set. More information: #3119 * Addressed comments: two values set is now type() == null instead of type() == UNKNOWN_TO_SDK_VERSION.
…f39ca924d Pull request: release <- staging/661c5916-0027-4e4d-9671-d58f39ca924d
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