`textinput.Model` doesn't seem to work well with append. about bubbles HOT 4 CLOSED

Oh wow! Thanks for your in depth explanation. Really appreciate it!

from bubbles.

Hi! You actually just need to copy the slice to avoid mutating it (since slices are pointers to arrays). There are a few ways to do this. Here's one example:

case "ctrl+q":
	m.inputs = append(m.inputs, textinput.Model{})           // increase the size of the slice by 1
	copy(m.inputs[m.focusIndex+1:], m.inputs[m.focusIndex:]) // shift the tail of the slice by 1
	m.inputs[m.focusIndex] = textinput.NewModel()            // insert a new textinput

from bubbles.

Hi, thanks for the reply! The solution works, that's super helpful!
I'm not sure how I mutated the models by appending some models to the tail of an existing slice, AFAIK, append only copies the structures that's passed in by value, so it shouldn't really modify anything. Do you mind pointing out where mutation happens?

from bubbles.

This isn't specific to textinput.Model. Rather, it's how slices work internally in Go. The arguments to append are indeed being passed by value, however slices are just structures that contain pointers to an underlying array. Internally Go represents slices more or less like this:

var underlyingArray [3]string

slice := struct{
    Length:        3,
    ZerothElement: &underlyingArray[0],
}

So if you slice that slice with slice := slice[1:] the representation becomes:

slice := struct{
    Length:        2,
    ZerothElement: &underlyingArray[1],
}

So in the case above, when you append to before you're inserting an element into the same underlying array that after is referencing. This causes after to suddenly be pointing to the wrong position in its underlying array, which happens to be the element that was just appended to before (example). Because of this, you need to use copy to create a new underlying array for after:

slice := []string{"a", "b", "c"}
index := 1

before := slice[:index]

// Copy the tail into a new slice so that it contains a separate underlying array.
after := make([]string, len(slice[index:]))
copy(after, slice[index:])

// Now you can safely append an element to the head and concatenate the two slices.
before = append(before, "NEW")
slice = append(before, after...)
fmt.Printf("%#v\n", slice)

(Playground)

I highly recommend reading Rob Pike's excellent blog post on how append work internally. It’s really good.

from bubbles.