Why Does My Go Code Produce a 'cannot use function (type func()) as type in argument' Error When Chaining Services with the asl Library?

"cannot use function (type func()) as type in argument"

This Go code aims to demonstrate chaining services by utilizing various functionalities like consuming messages, publishing messages, and replying to messages. The code employs the asl library for handling messaging operations.

When attempting to execute the code, an error message is encountered, indicating that the UpperCaseHandler and RepeatHandler functions cannot be used as arguments of type asl.MessageHandler in the ConsumeFunc method of the UpperCaser and Repeater services, respectively.

To resolve this issue, it is necessary to ensure that the function signatures match the expected format. The asl.MessageHandler type expects a function that takes a busboy.MessageDelivery as an argument and returns an interface{} and an error.

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

The UpperCaseHandler and RepeatHandler functions in your code are not conforming to this expected signature. They lack the error return value. To rectify this, modify the functions as follows:

func UpperCaseHandler(md busboy.MessageDelivery) (interface{}, error) {
     s.Reply(MessageTest{strings.ToUpper(md.Message.(string))}, md.Delivery)
     return nil, nil
}

func RepeatHandler(md busboy.MessageDelivery) (interface{}, error) {
     s.Reply(MessageTest{strings.Repeat(md.Message.(string), 5)}, md.Delivery)
     return nil, nil
}

By adding the error return value and ensuring a proper match with the asl.MessageHandler signature, the code should execute without encountering the aforementioned error.

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