How to Remove Elements from a Type-Asserted Slice of Interfaces in Go?

Removing Elements from Type Asserted Slice of Interfaces

When working with slices of interfaces in Go, one may need to remove or modify elements within them. However, directly assigning to the type-asserted slice can result in the error "cannot assign to value.([]interface {})".

This error occurs because interface values contain a copy of the wrapped value, not a reference to it. Therefore, attempts to modify the interface value will only affect the copy and not the original slice.

To remove an element from a type-asserted slice of interfaces, one must instead store a slice pointer in the interface. This allows for modifications to the pointed value, which is the actual slice.

Consider the following example:

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

var value interface{} = &s

// Remove the element at index 2 ("two")
sp := value.(*[]interface{})

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

fmt.Println(value)

In this code, the interface value value is assigned a slice pointer &s instead of the slice itself. The type assertion then retrieves the slice pointer from the interface. By modifying the dereferenced value *sp, the original slice is updated.

The output will be &[0 one 3 4], confirming that "two" has been removed from the slice. This technique allows for safe and effective modification of type-asserted slices of interfaces.

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