Why Can\'t You Get the Address of a Value Stored in a Go Interface?

Addressing Values Inside Interfaces

In order to understand why it's not feasible to take the address of a value stored in an interface, it's crucial to delve into the nature of an interface variable. Essentially, an interface value consists of two components:

• Type descriptor: This part specifies the type of the underlying value.
• Value/Pointer: Depending on the value's size, it either resides within the variable directly or a pointer to its storage is present.

Two key aspects to note:

1. The contained value belongs to the interface variable.
2. The value storage is subject to reuse for subsequent assignments.

Consider the following code snippet:

<code class="go">var v interface{}
v = int(42)
p := GetPointerToInterfaceValue(&v) // a pointer to an integer holding 42
v = &SomeStruct{...}</code>

In this scenario, the storage previously holding the integer is repurposed to store a pointer. As a result, dereferencing *p now yields the numeric representation of the pointer.

To prevent compromising the type system, Go intentionally restricts this type of pointer retrieval (apart from unsafe package usage).

Alternative Solutions

If your requirement is to access pointers of structs stored in a list, consider these alternatives:

• Store pointers to the structs instead of the struct values.
• Use *list.Element as a reference to the contained structures.

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