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-//
-// Now that we have optional types, we can apply them to structs.
-// The last time we checked in with our elephants, we had to link
-// all three of them together in a "circle" so that the last tail
-// linked to the first elephant. This is because we had NO CONCEPT
-// of a tail that didn't point to another elephant!
-//
-// We also introduce the handy ".?" shortcut:
-//
-// const foo = bar.?;
-//
-// is the same as
-//
-// const foo = bar orelse unreachable;
-//
-// See if you can find where we use this shortcut below.
-//
-// Now let's make those elephant tails optional!
-//
-const std = @import("std");
-
-const Elephant = struct {
- letter: u8,
- tail: *Elephant = null, // Hmm... tail needs something...
- visited: bool = false,
-};
-
-pub fn main() void {
- var elephantA = Elephant{ .letter = 'A' };
- var elephantB = Elephant{ .letter = 'B' };
- var elephantC = Elephant{ .letter = 'C' };
-
- // Link the elephants so that each tail "points" to the next.
- elephantA.tail = &elephantB;
- elephantB.tail = &elephantC;
-
- visitElephants(&elephantA);
-
- std.debug.print("\n", .{});
-}
-
-// This function visits all elephants once, starting with the
-// first elephant and following the tails to the next elephant.
-fn visitElephants(first_elephant: *Elephant) void {
- var e = first_elephant;
-
- while (!e.visited) {
- std.debug.print("Elephant {u}. ", .{e.letter});
- e.visited = true;
-
- // We should stop once we encounter a tail that
- // does NOT point to another element. What can
- // we put here to make that happen?
- if (e.tail == null) ???;
-
- e = e.tail.?;
- }
-}