WIP: switch to passing around a growable output object

[hadley]

This approach looks pretty performant — about 1µs per element

f <- function(n) {
  output <- growable()
  for (i in 1:n) output$push(1:10)
  output$get()
}
bench::mark(
  f(10),
  f(100),
  f(1000),
  check = FALSE
)
#> # A tibble: 3 × 3
#>   expression      min   median
#>   <bch:expr> <bch:tm> <bch:tm>
#> 1 f(10)       11.69µs  14.72µs
#> 2 f(100)     111.85µs  120.7µs
#> 3 f(1000)      1.14ms   1.18ms

[hadley]

Need to restore this.

[hadley]

There's a minor change of behaviour here in that evaluate("stop('x'); 1") previously would have printed 1, but that's not actually what you see if you type that at the console.

[hadley]

Closing since it's now split up into multiple PRs and my to do list 😄