Why Are My `UpperCaseHandler` and `RepeatHandler` Functions Incompatible with `asl.MessageHandler`?

Service Function Invocation: Argument Mismatch

In this code, you're facing an issue where the functions UpperCaseHandler and RepeatHandler are not compatible with the expected function signatures for asl.MessageHandler.

cannot use UpperCaseHandler (type func(asl.MessageDelivery)) as type asl.MessageHandler in assignment

cannot use RepeatHandler (type func(asl.MessageDelivery)) as type asl.MessageHandler in argument to Repeater.ConsumeFunc

Understanding Function Signatures

The asl.MessageHandler type expects functions with the following signature:

type MessageHandler func(MessageDelivery) (interface{}, error)

This means that these functions should take a single MessageDelivery struct as an argument and return both a result value (of any type) and an error (if there is one).

Correcting the Function Signatures

To resolve this issue, modify your UpperCaseHandler and RepeatHandler functions to match the expected signature:

func UpperCaseHandler(md asl.MessageDelivery) (interface{}, error) {
    s.Reply(MessageTest{strings.ToUpper(md.Message.(string))}, md.Delivery)
    // Modified to return nil, nil as the MessageDelivery struct is handled by the ASL library
    return nil, nil
}

func RepeatHandler(md asl.MessageDelivery) (interface{}, error) {
    s.Reply(MessageTest{strings.Repeat(md.Message.(string), 5)}, md.Delivery)
    // Modified to return nil, nil as the MessageDelivery struct is handled by the ASL library
    return nil, nil
}

With these changes, your functions will now match the expected signature and the code should run successfully.

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