Why Does My Struct Field Revert Unexpectedly in Go?

Struct Field Reverts Unexpectedly

In Go, structs are passed by value, meaning that changes made to a struct within a function are not reflected in the original struct. This becomes apparent in the provided code, where a struct field reverts to its original value even though the value was seemingly changed within a method.

The problem lies in how the struct is passed to the method. In the given code, the TVManager method sendMessage() is modifying a copy of the connector field, and any changes made inside the method are not propagated back to the original struct.

To fix this, the method should use a pointer receiver. By prefixing the receiver with an asterisk (*), the method will receive a pointer to the actual struct instance and any changes made within the method will be applied to the original struct.

func (this *TVManager) sendMessage(message string) {
    fmt.Println("5", this.connector)
    payload := map[string]string{
        "id":    "0",
        "type":  "request",
        "uri":   "ssap://system.notifications/createToast",
        "payload": "{'message': 'This is a message'}",
    }
    this.connector.sendCommand(payload)
    fmt.Println("4", this.connector)
}

Similarly, in the mock object, the sendCommand() method should also use a pointer receiver.

func (this *MockConnector) sendCommand(payload map[string]string) {
    fmt.Println("0", this)
    this.last_command = payload
    this.value = true
    fmt.Println("0", this)
}

Another Go convention is to avoid using "this" or "self" as receiver names. Instead, it's recommended to use a concise and descriptive name that matches the method's functionality.

By implementing these changes, the struct field will be successfully updated without reverting to its original value.

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