docs/development/languages/fidl/guides/compatibility/enum_flexible_strict.md

<!-- WARNING: This file is machine generated by //src/tests/fidl/source_compatibility/gen, do not edit. -->

Note: This document covers API impact only. For more details, see the
[ABI compatibility page](/docs/development/languages/fidl/guides/compatibility/README.md)

# Change an enum from flexible to strict

## Overview

-|[init](#init)|[step 1](#step-1)|[step 2](#step-2)|[step 3](#step-3)
---|---|---|---|---
fidl|[link](#fidl-init)||[link](#fidl-2)|
dart|[link](#dart-init)|[link](#dart-1)||
go|[link](#go-init)|[link](#go-1)||
hlcpp|[link](#hlcpp-init)|[link](#hlcpp-1)||
llcpp|[link](#llcpp-init)|[link](#llcpp-1)||
rust|[link](#rust-init)|[link](#rust-1)||[link](#rust-3)

## Initial State {#init}

### FIDL {#fidl-init}

```fidl
type Color = flexible enum : int32 {
    RED = 1;
    BLUE = 2;
};
```

### Dart {#dart-init}

```dart
fidllib.Color complement(fidllib.Color color) {
  if (color.isUnknown()) {
    return color;
  }
  switch (color) {
    case fidllib.Color.blue:
      return fidllib.Color.red;
    case fidllib.Color.red:
      return fidllib.Color.blue;
    default:
      return null;
  }
}

```

### Go {#go-init}

```go
func complement(color lib.Color) lib.Color {
	if color.IsUnknown() {
		return color
	}
	switch color {
	case lib.ColorBlue:
		return lib.ColorRed
	case lib.ColorRed:
		return lib.ColorBlue
	default:
		return color
	}
}

```

### HLCPP {#hlcpp-init}

```cpp
fidl_test::Color complement(fidl_test::Color color) {
  if (color.IsUnknown()) {
    return color;
  }
  switch (color) {
    case fidl_test::Color::RED:
      return fidl_test::Color::BLUE;
    case fidl_test::Color::BLUE:
      return fidl_test::Color::RED;
    default:
      return color;
  }
}
```

### LLCPP {#llcpp-init}

```cpp
fidl_test::wire::Color complement(fidl_test::wire::Color color) {
  if (color.IsUnknown()) {
    return color;
  }
  switch (color) {
    case fidl_test::wire::Color::kRed:
      return fidl_test::wire::Color::kBlue;
    case fidl_test::wire::Color::kBlue:
      return fidl_test::wire::Color::kRed;
    default:
      return color;
  }
}
```

### Rust {#rust-init}

```rust
fn complement(color: &fidl_lib::Color) -> Option<fidl_lib::Color> {
    match color.validate() {
        Ok(fidl_lib::Color::Red) => Some(fidl_lib::Color::Blue),
        Ok(fidl_lib::Color::Blue) => Some(fidl_lib::Color::Red),
        _ => None,
    }
}

```

## Update Source Code {#step-1}

### Dart {#dart-1}


```diff
  fidllib.Color complement(fidllib.Color color) {
-   if (color.isUnknown()) {
-     return color;
-   }
+   assert(color.isUnknown() == false);
    switch (color) {
      case fidllib.Color.blue:
        return fidllib.Color.red;
      case fidllib.Color.red:
        return fidllib.Color.blue;
      default:
        return null;
    }
  }
  

```

### Go {#go-1}

- Remove usages of any flexible specific APIs

```diff
  func complement(color lib.Color) lib.Color {
- 	if color.IsUnknown() {
- 		return color
- 	}
  	switch color {
  	case lib.ColorBlue:
  		return lib.ColorRed
  	case lib.ColorRed:
  		return lib.ColorBlue
  	default:
  		return color
  	}
  }
  

```

### HLCPP {#hlcpp-1}

- Remove usages of any flexible specific APIs

```diff
  fidl_test::Color complement(fidl_test::Color color) {
-   if (color.IsUnknown()) {
-     return color;
-   }
    switch (color) {
      case fidl_test::Color::RED:
        return fidl_test::Color::BLUE;
      case fidl_test::Color::BLUE:
        return fidl_test::Color::RED;
      default:
        return color;
    }
  }

```

### LLCPP {#llcpp-1}

- Remove usages of any flexible specific APIs

```diff
  fidl_test::wire::Color complement(fidl_test::wire::Color color) {
-   if (color.IsUnknown()) {
-     return color;
-   }
    switch (color) {
      case fidl_test::wire::Color::kRed:
        return fidl_test::wire::Color::kBlue;
      case fidl_test::wire::Color::kBlue:
        return fidl_test::wire::Color::kRed;
      default:
        return color;
    }
  }

```

### Rust {#rust-1}

- Remove usages of any flexible specific APIs
- Allow unreachable patterns and add an underscore arm to any `match` statements on the enum.

```diff
  fn complement(color: &fidl_lib::Color) -> Option<fidl_lib::Color> {
-     match color.validate() {
-         Ok(fidl_lib::Color::Red) => Some(fidl_lib::Color::Blue),
-         Ok(fidl_lib::Color::Blue) => Some(fidl_lib::Color::Red),
+     #[allow(unreachable_patterns)]
+     match color {
+         fidl_lib::Color::Red => Some(fidl_lib::Color::Blue),
+         fidl_lib::Color::Blue => Some(fidl_lib::Color::Red),
          _ => None,
      }
  }
  

```

## Update FIDL Library {#step-2}

- Change from `flexible` to `strict`

```diff
- type Color = flexible enum : int32 {
+ type Color = strict enum : int32 {
      RED = 1;
      BLUE = 2;
  };

```

## Update Source Code {#step-3}

### Rust {#rust-3}

- Remove the unreachable patterns attribute and underscore arm.

```diff
- fn complement(color: &fidl_lib::Color) -> Option<fidl_lib::Color> {
-     #[allow(unreachable_patterns)]
+ fn complement(color: &fidl_lib::Color) -> fidl_lib::Color {
      match color {
-         fidl_lib::Color::Red => Some(fidl_lib::Color::Blue),
-         fidl_lib::Color::Blue => Some(fidl_lib::Color::Red),
-         _ => None,
+         fidl_lib::Color::Red => fidl_lib::Color::Blue,
+         fidl_lib::Color::Blue => fidl_lib::Color::Red,
      }
  }
  

```