Can You Take the Address of a Value Inside an Interface in Go?

Taking Address of Value Inside an Interface

In the context of the Go programming language, an interface acts as a contract, defining a set of methods that a type must implement. When a value is assigned to an interface, it is wrapped in an interface value. However, the interface value itself does not store the actual value but holds a reference to it.

Therefore, attempting to take the address of a value inside an interface using the & operator will result in an error, as demonstrated in the following code snippet:

<code class="go">import "container/list"

type retry struct{}

var el = list.Element{Value: retry{}}

p := &el.Value.(retry) // Compilation error: cannot take the address of el.Value.(retry)</code>

This error stems from the fact that the value inside the interface is owned by the interface value itself, and its storage may be reused when a new value is assigned to the interface. Modifying the value at the obtained address would directly affect the interface value, which is undesirable and could lead to unexpected behavior.

To address this situation, there are alternative approaches available:

Store Pointers Instead of Values:
Instead of storing struct values directly in the interface, one can store pointers to those structs. This ensures that the pointer remains valid even if the interface value changes.

Use Element References:
Another option is to pass *list.Element values as references to the contained structures. This effectively provides indirect access to the struct values without violating Go's type safety.

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