Note: This document covers API impact only. For more details, see the ABI compatibility page
Change a union from flexible to strict
Overview
- | init | step 1 | step 2 | step 3 |
---|---|---|---|---|
fidl | link | link | ||
dart | link | link | link | |
go | link | link | ||
hlcpp | link | link | link | |
llcpp | link | link | link | |
rust | link | link | link |
Initial State {#init}
FIDL {#fidl-init}
flexible union JsonValue {
1: int32 int_value;
2: string:MAX string_value;
};
Dart {#dart-init}
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: ${value.stringValue}');
break;
case fidllib.JsonValueTag.$unknown:
print('unknown variant: ${value.$unknownData}');
break;
}
}
Go {#go-init}
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 {#hlcpp-init}
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;
case fidl_test::JsonValue::Tag::kUnknown:
printf("<%lu unknown bytes>\n", value.UnknownBytes()->size());
break;
}
}
LLCPP {#llcpp-init}
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().data());
break;
case fidl_test::JsonValue::Tag::kUnknown:
printf("<unknown data>\n");
break;
}
}
Rust {#rust-init}
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),
fidl_lib::JsonValueUnknown!() => println!("<unknown union>"),
};
}
Update Source Code {#step-1}
Dart {#dart-1}
- Replace the unknown tag with a default case in any switch statements
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: ${value.stringValue}');
break;
- case fidllib.JsonValueTag.$unknown:
+ default:
+ // Note: unknown variants will fail to decode until the union is marked flexible
print('unknown variant: ${value.$unknownData}');
break;
}
}
Go {#go-1}
- Remove usages of 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 {#hlcpp-1}
- Replace the
kUnknown
tag with a default case in any switch statements - Remove usages of 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;
- case fidl_test::JsonValue::Tag::kUnknown:
- printf("<%lu unknown bytes>\n", value.UnknownBytes()->size());
- break;
+ default:
+ printf("<unknown variant>\n");
}
}
LLCPP {#llcpp-1}
- Replace the
kUnknown
tag with a default case in any switch statements - Remove usages of 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().data());
break;
- case fidl_test::JsonValue::Tag::kUnknown:
- printf("<unknown data>\n");
- break;
+ default:
+ printf("<unknown variant>\n");
}
}
Rust {#rust-1}
- 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),
- fidl_lib::JsonValueUnknown!() => println!("<unknown union>"),
+ _ => {}
};
}
Update FIDL Library {#step-2}
- Change the union from
flexible
tostrict
- flexible union JsonValue {
+ strict union JsonValue {
1: int32 int_value;
2: string:MAX string_value;
};
Update Source Code {#step-3}
Dart {#dart-3}
- You can now remove the default case in any switch statements
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 {#hlcpp-3}
- You can now remove the default case
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 {#llcpp-3}
- You can now remove the default case
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().data());
break;
- default:
- printf("<unknown variant>\n");
}
}
Rust {#rust-3}
- Remove the attribute and underscore arm
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),
- _ => {}
};
}