Golang slice append gotcha

  • use append only to append new value to given slice, not to create new one:
someSlice = append(someSlice, newElement)
  • if you want to create new slice based on old one with some appended value, always copy it first (example function credits go to SO user):
func copyAndAppend(i []int, vals ...int) []int {
j := make([]int, len(i), len(i)+len(vals))
copy(j, i)
return append(j, vals...)
}
newSlice := append(T(nil), oldSlice...)

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