Support automatic string‑based selectors (inline select)

[azalessky]

Motivation

Currently, when defining a selector with param=room in JSON:

{
  "notification": {
    "lessonBody(param=room)": {
      "empty": "$time",
      "other": "$time • room $room"
    }
  }
}

Slang generates two separate methods (empty(...) and other(...)). The developer must manually decide which one to call in code.

It would be useful to have an inline selector feature, similar to ICU select, where the generator produces one method (e.g. lessonBody(...)) and automatically chooses the correct branch based on the parameter value.

Developer Experience

Proposed syntax:

{
  "notification": {
    "lessonBody(select, param=room)": {
      "empty": "$time",
      "other": "$time • room $room"
    }
  }
}

Expected generated API:

String lessonBody({required DateTime time, required String room});

Usage:

final body = t.notification.lessonBody(time: lesson.start, room: lesson.room);

If room is empty → returns $time.
If room is non‑empty → returns $time • room $room.

Benefits

• Cleaner developer experience.
• Less duplication in generated code.
• More intuitive for those familiar with ICU select.
• Consistent handling of string‑based conditions (empty/non‑empty, status values, gender, etc.).

[Tienisto]

Hi, enums are implemented as context in Slang which works with enums like gender.

Have you tried:

{
  "lessonBody(context=RoomType)": {
    "empty": "$time",
    "other": "$time • room $room"
  }
}

Edit:

Is your proposed select possible in ICU? I thought select requires a concrete enum like https://support.crowdin.com/icu-message-syntax/#select

[azalessky]

Thanks for the example!
But my original question was about a string (room), not an enum context. Using RoomType is a slightly different scenario, while I wanted to understand whether select can be applied directly to a string value.

[Tienisto]

I see. It is basically a switch block using strings instead of enums. The official ICU spec does not contain empty though.
Based on ICU:

{gender, select, 
  male {He}
  female {She}
  other {They}
} will respond soon.

It would treat any string s == 'male' so also s == 'empty'. Only other is a reserved keyword according to ICU.

Can you provide examples from other i18n solutions that uses select with empty?

[azalessky]

You're absolutely right about the ICU spec - select doesn't include an empty keyword. I added it as a proposed extension to handle null/empty string cases more elegantly.

However, the core issue remains: currently slang doesn't provide any string-based selector functionality. The workaround with concatenation is quite verbose:

// Current workaround
final result = switch(myString) {
  'value1' => t.somePath.value1,
  'value2' => t.somePath.value2,
  _ => t.somePath.other,
};