Overview
Initial State
FIDL
type JsonValue = strict union {
1: int_value int32;
2: string_value string:MAX;
};
Dart
void useUnion(fidllib.JsonValue value) {
assert(value.$unknownData == null);
switch (value.$tag) {
case fidllib.JsonValueTag.intValue:
print('int value: ${value.intValue}');
break;
case fidllib.JsonValueTag.stringValue:
print('string value: ${value.stringValue}');
break;
}
}
Go
func useUnion(value lib.JsonValue) {
switch value.Which() {
case lib.JsonValueIntValue:
fmt.Printf("int value: %d\n", value.IntValue)
case lib.JsonValueStringValue:
fmt.Printf("string value: %s\n", value.StringValue)
default:
fmt.Println("unknown tag")
}
}
HLCPP
void use_union(fidl_test::JsonValue value) {
switch (value.Which()) {
case fidl_test::JsonValue::Tag::kIntValue:
printf("int value: %d\n", value.int_value());
break;
case fidl_test::JsonValue::Tag::kStringValue:
printf("string value: %s\n", value.string_value().c_str());
break;
case fidl_test::JsonValue::Tag::Invalid:
printf("<uninitialized union>\n");
break;
}
}
LLCPP
void use_union(fidl_test::wire::JsonValue* value) {
switch (value->which()) {
case fidl_test::wire::JsonValue::Tag::kIntValue:
printf("int value: %d\n", value->int_value());
break;
case fidl_test::wire::JsonValue::Tag::kStringValue:
printf("string value: %s\n", value->string_value().data());
break;
}
}
Rust
fn use_union(value: &fidl_lib::JsonValue) {
match value {
fidl_lib::JsonValue::IntValue(n) => println!("int value: {}", n),
fidl_lib::JsonValue::StringValue(s) => println!("string: {}", s),
};
}
Update Source Code
Dart
- Add a default case to any switch statements on the union to handle new unknown variants
void useUnion(fidllib.JsonValue value) {
- assert(value.$unknownData == null);
switch (value.$tag) {
case fidllib.JsonValueTag.intValue:
print('int value: ${value.intValue}');
break;
case fidllib.JsonValueTag.stringValue:
print('string value: ${value.stringValue}');
break;
+ default:
+ // Note: unknown variants will fail to decode until the union is marked flexible
+ print('unknown variant: ${value.$unknownData}');
+ break;
}
}
HLCPP
- Add a default case to any switch statements on the union to handle new unknown variants
void use_union(fidl_test::JsonValue value) {
switch (value.Which()) {
case fidl_test::JsonValue::Tag::kIntValue:
printf("int value: %d\n", value.int_value());
break;
case fidl_test::JsonValue::Tag::kStringValue:
printf("string value: %s\n", value.string_value().c_str());
break;
case fidl_test::JsonValue::Tag::Invalid:
printf("<uninitialized union>\n");
break;
+ default:
+ printf("<unknown variant>\n");
}
}
LLCPP
- Add a default case to any switch statements on the union to handle new unknown variants
void use_union(fidl_test::wire::JsonValue* value) {
switch (value->which()) {
case fidl_test::wire::JsonValue::Tag::kIntValue:
printf("int value: %d\n", value->int_value());
break;
case fidl_test::wire::JsonValue::Tag::kStringValue:
printf("string value: %s\n", value->string_value().data());
break;
+ default:
+ printf("<unknown variant>\n");
}
}
Rust
- Add
[allow(unreachable_patterns)] and an underscore arm to match statements on the union
fn use_union(value: &fidl_lib::JsonValue) {
+ #[allow(unreachable_patterns)]
match value {
fidl_lib::JsonValue::IntValue(n) => println!("int value: {}", n),
fidl_lib::JsonValue::StringValue(s) => println!("string: {}", s),
+ _ => {}
};
}
Update FIDL Library
- Change the union from
strict to flexible
- type JsonValue = strict union {
+ type JsonValue = flexible union {
1: int_value int32;
2: string_value string:MAX;
};
Update Source Code
Dart
- Replace the default case with the unknown tag.
void useUnion(fidllib.JsonValue value) {
switch (value.$tag) {
case fidllib.JsonValueTag.intValue:
print('int value: ${value.intValue}');
break;
case fidllib.JsonValueTag.stringValue:
print('string value: ${value.stringValue}');
break;
- default:
- // Note: unknown variants will fail to decode until the union is marked flexible
+ case fidllib.JsonValueTag.$unknown:
print('unknown variant: ${value.$unknownData}');
break;
}
}
Go
- You may now use any flexible union specific APIs
func useUnion(value lib.JsonValue) {
switch value.Which() {
case lib.JsonValueIntValue:
fmt.Printf("int value: %d\n", value.IntValue)
case lib.JsonValueStringValue:
fmt.Printf("string value: %s\n", value.StringValue)
+ case lib.JsonValue_unknownData:
+ fmt.Printf("unknown data: %+v\n", value.GetUnknownData())
default:
fmt.Println("unknown tag")
}
}
HLCPP
- Replace the default case with the
kUnknown tag.
- You may now use any flexible union specific APIs
void use_union(fidl_test::JsonValue value) {
switch (value.Which()) {
case fidl_test::JsonValue::Tag::kIntValue:
printf("int value: %d\n", value.int_value());
break;
case fidl_test::JsonValue::Tag::kStringValue:
printf("string value: %s\n", value.string_value().c_str());
break;
case fidl_test::JsonValue::Tag::Invalid:
printf("<uninitialized union>\n");
break;
- default:
- printf("<unknown variant>\n");
+ case fidl_test::JsonValue::Tag::kUnknown:
+ printf("<%lu unknown bytes>\n", value.UnknownBytes()->size());
+ break;
}
}
LLCPP
- Replace the default case with the
kUnknown tag.
- You may now use any flexible union specific APIs
void use_union(fidl_test::wire::JsonValue* value) {
switch (value->which()) {
case fidl_test::wire::JsonValue::Tag::kIntValue:
printf("int value: %d\n", value->int_value());
break;
case fidl_test::wire::JsonValue::Tag::kStringValue:
printf("string value: %s\n", value->string_value().data());
break;
- default:
- printf("<unknown variant>\n");
+ case fidl_test::wire::JsonValue::Tag::kUnknown:
+ printf("<unknown data>\n");
+ break;
}
}
Rust
- Remove the attribute and replace the underscore arm with the generated macro to match against unknown variants
fn use_union(value: &fidl_lib::JsonValue) {
- #[allow(unreachable_patterns)]
match value {
fidl_lib::JsonValue::IntValue(n) => println!("int value: {}", n),
fidl_lib::JsonValue::StringValue(s) => println!("string: {}", s),
- _ => {}
+ fidl_lib::JsonValueUnknown!() => println!("<unknown union>"),
};
}
