How to Access Fields of an Anonymous Struct Passed as an Interface with No Methods in Golang?

Interface with No Methods: Accessing Custom Type in Golang

In Golang, you can create anonymous structs and pass them as arguments to functions that accept an interface type. However, if the interface doesn't have any methods defined, you won't be able to directly access the fields of the anonymous struct.

Consider the following code example:

<code class="go">func NewJob(t string, name string, c func(), v interface{}) {
    // ...
}

func Custom(name string) interface{} {
    // ...
}

main() {
    gojob.NewJob("every 2 seconds", "pene", func() {
        t := gojob.Custom("pene")
        fmt.Println(t) // Prints "{1}"
        fmt.Println(t.Id) // Error: t.Id undefined (type interface {} is interface with no methods)
    }, struct {
        Id int
    }{
        1,
    })
}</code>

In this example, we're passing an anonymous struct as the v argument to NewJob. The function Custom retrieves the custom value associated with the name "pene" and returns it as an interface{}.

When we try to access the Id field of the anonymous struct within the goroutine, we encounter the error "t.Id undefined". This is because the interface{} type has no defined methods, so we can't treat it like a concrete type.

To access the fields of the anonymous struct, we need to type assert it to a compatible type. In this case, we know that v contains an anonymous struct with an Id field of type int. We can type assert it using the following syntax:

<code class="go">id := v.(struct{Id int}).Id</code>

This will convert the interface{} value v into a concrete struct with an Id field, allowing us to access it directly.

By type asserting the interface{} value, we can access the fields of the anonymous struct and use them as needed.

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