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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) break;
e = e.tail.?;
}
}
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