Here are a few question-based titles that capture the essence of your article: * How do I Set an Interface or Pointer to Nil in Golang? * Golang Nil Assignment: Interfaces vs. Pointers: What\'s the

How to Set an Interface or Pointer to Nil in Golang

In Golang, setting an interface value to nil may not be as straightforward as expected. This article discusses how to set interfaces and pointers to nil in different scenarios.

Setting an Interface to Nil

When dealing with an interface value, specifically an interface that holds a concrete type, the correct approach is to pass a pointer to the interface rather than the interface value itself. To set an interface to nil, use a function that accepts an interface pointer, such as:

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

Example:

<code class="go">var i interface{} = "Bob"
setNilIf(&i)
fmt.Println(i) // Prints <nil></nil></code>

Setting a Pointer to Nil

Unsetting a pointer value requires a bit more effort. Since pointers are essentially memory addresses, we need to dereference the pointer to actually modify the value. This introduces an issue because unsafe.Pointer cannot be dereferenced directly. To resolve this, we can use the following function:

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

Example:

<code class="go">typ := &TYP{InternalState: "filled"}
fmt.Println(typ) // Prints &{filled}
setNilPtr(unsafe.Pointer(&typ))
fmt.Println(typ) // Prints <nil></nil></code>

Note: For the sake of simplicity, the example uses int as the target type for dereferencing. Any pointer type can be used as the target.

Alternatively, you can use reflection to nil a pointer:

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

Example:

<code class="go">typ2 := &TYP{InternalState: "filled"}
fmt.Println(typ2) // Prints &{filled}
setNilPtr2(typ2)
fmt.Println(typ2) // Prints <nil></nil></code>

Best Practice

While the techniques described above provide ways to set interfaces and pointers to nil, it's best to use the idiomatic approach, which is to simply assign nil to the value. For example:

<code class="go">// Set interface to nil
i = nil

// Set pointer to nil
typ = nil</code>

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