Added ex. 46 optionals 2 - elephants!

This commit is contained in:
Dave Gauer 2021-02-16 20:21:32 -05:00
parent efdcfc70d4
commit f27601b558
4 changed files with 64 additions and 1 deletions

View file

@ -240,7 +240,11 @@ const exercises = [_]Exercise{
.main_file = "45_optionals.zig",
.output = "The Ultimate Answer: 42.",
},
// optional fields (elephant tail - no longer need circular)
.{
.main_file = "46_optionals2.zig",
.output = "Elephant A. Elephant B. Elephant C.",
.hint = "Elephants!",
},
// super-simple struct method
// use struct method for elephant tails
// quiz: add elephant trunk (like tail)!

View file

@ -28,6 +28,8 @@ pub fn main() void {
elephantC.tail = &elephantA;
visitElephants(&elephantA);
std.debug.print("\n", .{});
}
// This function visits all elephants once, starting with the

View file

@ -0,0 +1,46 @@
//
// 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!
//
const std = @import("std"); // single quotes
const Elephant = struct {
letter: u8,
tail: *Elephant = undefined, // <---- make this optional!
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.?;
}
}

View file

@ -0,0 +1,11 @@
12c12
< tail: *Elephant = undefined, // <---- make this optional!
---
> tail: ?*Elephant = undefined,
39,42c39
< // 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) ???;
---
> if (e.tail == null) break;