How do you nullify an interface in Golang?

Nullifying an Interface in Golang

Problem:

Attempting to nullify an internal value of an interface raises the question: how to implement such a function, setNil(typ interface{})?

Answer:

To effectively nullify an interface, it's crucial to remember that working with a pointer value is different from working with an interface value. As pointers are passed by reference, a pointer to the interface must be passed to modify its internal state.

Function for Nullification of Interface{}:

<code class="go">func setNilIf(v *interface{}) {
    *v = nil
}</code>

Usage:

<code class="go">var i interface{} = "Bob"
fmt.Printf("Before: %v\n", i)
setNilIf(&i)
fmt.Printf("After: %v\n", i)</code>

Output:

Before: Bob
After: <nil></nil>

Function for Nullification of Pointers (Unsafe.Pointer):

To nullify a pointer, it can be converted to an unsafe.Pointer and dereferenced:

<code class="go">func setNilPtr(p unsafe.Pointer) {
    *(**int)(p) = nil
}</code>

Usage:

<code class="go">typ := &TYP{InternalState: "filled"}
fmt.Printf("Before: %v\n", typ)
setNilPtr(unsafe.Pointer(&typ))
fmt.Printf("After: %v\n", typ)</code>

Output:

Before: &{filled}
After: <nil></nil>

Function for Nullification of Pointers (Reflection):

Finally, reflection can also be used to nullify a pointer:

<code class="go">func setNilPtr2(i interface{}) {
    v := reflect.ValueOf(i)
    v.Elem().Set(reflect.Zero(v.Elem().Type()))
}</code>

Usage:

<code class="go">typ2 := &TYP{InternalState: "filled"}
fmt.Printf("Before: %v\n", typ2)
setNilPtr2(&typ2)
fmt.Printf("After: %v\n", typ2)</code>

Output:

Before: &{filled}
After: <nil></nil>

However, for simplicity, it's recommended to directly assign nil to nullify a pointer:

<code class="go">i = nil
typ = nil</code>

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