Transform the value.

Alias to ref.

Call the function on the content of the reference.

Update the reference's content with the given function.

incr_then_get r increments r and returns its new value, think ++r.

• since 0.17

get_then_incr r increments r and returns its old value, think r++.

• since 0.17

swap t1 t2 puts !t2 in t1 and !t1 in t2.

• since 1.4

protect r x f sets r := x; calls f(); restores r to its old value; and returns the result of f().

• since 3.10

• since 3.0