How to Modify Type-Asserted Slices of Interfaces in Go?

Manipulating Type-Asserted Slices of Interfaces in Go

In Golang, type assertion allows developers to access the underlying concrete type of an interface value. However, it is important to note that type assertion does not modify the original interface value. This can be problematic when attempting to remove elements from a type-asserted slice of interfaces.

Consider the following example:

value := []interface{}{0, "one", "two", 3, 4}

If we attempt to remove an element from the slice using the type assertion:

i := 2
value.([]interface{}) = append(value.([]interface{})[:i],
   value.([]interface{})[i+1:]...)

We will encounter an error stating "cannot assign to value (type []interface {})". This is because type assertion creates a copy of the original value, and changes made to the copy do not affect the original.

To address this issue, it is necessary to modify an underlying slice of interfaces rather than type-asserted copies. This can be achieved by wrapping the slice in an interface pointer:

value := []*[]interface{}{&[]interface{}{0, "one", "two", 3, 4}}

Using the pointer allows us to modify the underlying slice:

sp := value[0]
i := 2
*sp = append((*sp)[:i], (*sp)[i+1:]...)

In this case, the changes made to the pointed slice are reflected in the original interface value:

fmt.Println(value)
// Output: [*[]interface {0 one 3 4}]

By utilizing interface pointers, developers can manipulate type-asserted slices of interfaces without encountering assignment errors.

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