Remove elements from a slice, then return the removed and remaining elements

Just use the range to get the value and the index instead of accessing the value by using the index.

package main

import (
    "fmt"
)

func main() {
    var names = []string{"john", "julio", "pepito", "carlos"}
    name, newNames, _ := getMe("john", names)

    fmt.Println("extracted name:\t\t\t\t", name)
    fmt.Println("new slice without extracted name:\t", newNames)
    fmt.Println("old slice still intact:\t\t\t", names)
}

func getMe(me string, names []string) (string, []string, bool) {
    var newSlice []string

    for i := 0; i < len(names); i++ {
        if names[i] == me {
            newSlice = append(newSlice, names[:i]...)
            newSlice = append(newSlice, names[i+1:]...)
            return names[i], newSlice, true
        }
    }

    return "", nil, false
}

output

extracted name:                        john
new slice without extracted name:      [julio pepito carlos]
old slice still intact:                [john julio pepito carlos]

See playground example

Edited after request for a faster version: it's much faster to use a manual instead of a range loop. Since you need to create a new slice with no elements, it is necessary to build a new slice inside the function, which always requires some processing power.