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Complex Unions

Typr Events handles Avro unions beyond simple ["null", T] optionals.

Simple Nullable Fields​

The most common union - nullable fields:

{"name": "email", "type": ["null", "string"], "default": null}

Generates idiomatic optional types:

  • Java: Optional<String>
  • Kotlin: String?
  • Scala: Option[String]

Multi-Type Unions​

Unions with multiple non-null types generate sealed types:

Schema​

{
  "name": "value",
  "type": ["string", "int", "boolean"]
}

Generated (Java)​

public sealed interface StringOrIntOrBoolean
    permits StringOrIntOrBoolean.StringValue,
            StringOrIntOrBoolean.IntValue,
            StringOrIntOrBoolean.BooleanValue {

    record StringValue(String value) implements StringOrIntOrBoolean {}
    record IntValue(int value) implements StringOrIntOrBoolean {}
    record BooleanValue(boolean value) implements StringOrIntOrBoolean {}
}

Generated (Kotlin)​

sealed interface StringOrIntOrBoolean {
    @JvmInline value class StringValue(val value: String) : StringOrIntOrBoolean
    @JvmInline value class IntValue(val value: Int) : StringOrIntOrBoolean
    @JvmInline value class BooleanValue(val value: Boolean) : StringOrIntOrBoolean
}

Generated (Scala)​

enum StringOrIntOrBoolean:
  case StringValue(value: String)
  case IntValue(value: Int)
  case BooleanValue(value: Boolean)

Usage​

Creating​

StringOrIntOrBoolean value1 = new StringOrIntOrBoolean.StringValue("hello");
StringOrIntOrBoolean value2 = new StringOrIntOrBoolean.IntValue(42);
StringOrIntOrBoolean value3 = new StringOrIntOrBoolean.BooleanValue(true);

Pattern Matching​

switch (value) {
    case StringOrIntOrBoolean.StringValue(var s) -> process(s);
    case StringOrIntOrBoolean.IntValue(var i) -> process(i);
    case StringOrIntOrBoolean.BooleanValue(var b) -> process(b);
}

Named Record Unions​

Unions of named records generate a sealed interface:

Schema​

{
  "name": "identifier",
  "type": ["string", "long"]
}

With x-typr-wrapper:

{
  "name": "identifier",
  "type": ["string", "long"],
  "x-typr-union-name": "Identifier"
}

Generated​

public sealed interface Identifier
    permits Identifier.StringId, Identifier.LongId {

    record StringId(String value) implements Identifier {}
    record LongId(long value) implements Identifier {}
}

Nullable Multi-Type Unions​

Unions with null and multiple types:

{"type": ["null", "string", "int"]}

Generates Optional<StringOrInt> (Java) or StringOrInt? (Kotlin).

Dynamic Values​

For truly dynamic JSON-like structures:

{
  "name": "metadata",
  "type": ["null", "string", "long", "double", "boolean",
           {"type": "array", "items": "DynamicValue"},
           {"type": "map", "values": "DynamicValue"}]
}

Generates a DynamicValue type that can hold any of these recursively.