59 lines
1.6 KiB
Zig
59 lines
1.6 KiB
Zig
//
|
|
// 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.?;
|
|
}
|
|
}
|