devtools::load_all("~/packages/ggplot2")
#> ℹ Loading ggplot2

ggplot(mapping = aes(x = 0, xend = 1)) +
  geom_segment(
    aes(y = 0, yend = 0, colour = "arrow 1"),
    arrow = arrow(length = unit(1, "cm"), angle = 10)
  ) +
  geom_segment(
    aes(y = 1, yend = 1, colour = "arrow 2"),
    arrow = arrow(length = unit(1, "cm"), angle = 70, ends = "both")
  ) +
  geom_segment(
    aes(y = 2, yend = 2, colour = "arrow 3"),
    arrow = arrow(length = unit(1, "cm"), angle = 45, ends = "first")
  )