       iex> String.replace_prefix("hello hello world", "hello ", "ola ")
       "ola hello world"
 
+      iex> String.replace_prefix("world", "", "hello ")
+      "hello world"
+
   """
   @spec replace_prefix(t, t, t) :: t
   def replace_prefix(string, match, replacement)

  @doc """
  Replaces prefix in `string` by `replacement` if it matches `match`.

  Returns the string untouched if there is no match.

  ## Examples


      "hello mundo"
      iex> String.replace_suffix("hello world world", " world", " mundo")
      "hello world mundo"

      iex> String.replace_suffix("hello", "", " world")
      "hello world"

  """
  @spec replace_suffix(t, t, t) :: t
