Allow switch expression branches to have bodies

[ktkk]

Sometimes I want to do just a little bit more in one branch of a switch expression compared to another.
Let's say I want to log something when a Success branch is reached.

Currently I have 2 options:

1. Convert the switch expression to a switch statement:

final String message;
switch (result) {
    case Success(success: final success):
        developer.log(success);
        message = success;
    case Error(error: final error):
        throw error;
}

2. Write a separate function for the Success branch

final message = switch (result) {
    Success(success: final success) => _logAndReturn(success),
    Error(error: final error) => throw error,
};

String _logAndReturn(String message) {
    developer.log(message);
    return message;
}

I find the first option a bit too verbose and the second option difficult to read because it requires you to navigate to the function to know what's going on.

So why not allow switch expressions to have bodies?

final message = switch (result) {
    Success(success: final success) => {
        developer.log(success);
        success
    },
    Error(error: final error) => throw error,
};

This would make Dart's switch expression more similar to Rust's match or Kotlin's when.
Additionally, it could introduce implicit returns from functions like Rust or just from lambdas like Kotlin, because currently the syntax looks a bit out of place in Dart.

[elliotPopina]

Hi @ktkk i have the same problem, to overcome this I do like this

final message = switch (result) {
    Success(success: final success) =>  () {
        developer.log(success);
        return success
    }.call(),
    Error(error: final error) => throw error,
};

Hope this help you

[ktkk]

Hi @elliotPopina,
That's indeed a good solution.
Would still be nice if this was a native language feature instead of a workaround like this :)

[mateusfccp]

Duplicate of #3117.

[mateusfccp]

Hi @ktkk i have the same problem, to overcome this I do like this

final message = switch (result) {
    Success(success: final success) =>  () {
        developer.log(success);
        return success
    }.call(),
    Error(error: final error) => throw error,
};

Hope this help you

You don't need to use .call():

final message = switch (result) {
    Success(success: final success) =>  () {
        developer.log(success);
        return success
    }(),
    Error(error: final error) => throw error,
};

Although, I don't recommend. Expressions should be pure.

If you need multiple lines, use a switch statement.