Added ex 48, additional comment on 46

This commit is contained in:
Dave Gauer 2021-02-28 13:23:22 -05:00
parent 11ec69b92c
commit 5f7e9389d5
6 changed files with 112 additions and 7 deletions

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@ -127,7 +127,7 @@ Planned exercises:
* [x] Structs
* [x] Pointers
* [x] Optionals
* [ ] Struct methods
* [x] Struct methods
* [ ] Slices
* [ ] Multi pointers
* [ ] Unions

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@ -250,8 +250,16 @@ const exercises = [_]Exercise{
.output = "5 aliens. 4 aliens. 1 aliens. 0 aliens. Earth is saved!",
.hint = "Use the heat ray. And the method!",
},
// use struct method for elephant tails
// quiz: add elephant trunk (like tail)!
.{
.main_file = "48_methods2.zig",
.output = "Elephant A (U). Elephant B (U). Elephant C (U).",
.hint = "This just needs one little fix."
},
// 48 use struct method for elephant tails
// 49 quiz: add elephant trunk (like tail)!
// 50 null vs undefined
// 51 pass-by-value and const fn params
// 52 slices!
};
/// Check the zig version to make sure it can compile the examples properly.

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@ -5,11 +5,23 @@
// 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, // <---- make this optional!
tail: *Elephant = null, // Hmm... tail needs something...
visited: bool = false,
};

68
exercises/48_methods2.zig Normal file
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@ -0,0 +1,68 @@
//
// Now that we've seen how methods work, let's see if we can help
// our elephants out a bit more with some Elephant methods.
//
const std = @import("std");
const Elephant = struct {
letter: u8,
tail: ?*Elephant = null,
visited: bool = false,
// New Elephant methods!
pub fn getTail(self: *Elephant) *Elephant {
return self.tail.?; // Remember, this is means "orelse unreachable"
}
pub fn hasTail(self: *Elephant) bool {
return (self.tail != null);
}
pub fn visit(self: *Elephant) void {
self.visited = true;
}
pub fn print(self: *Elephant) void {
// Prints elephant letter and (V)isited or (U)nvisited.
var v: u8 = if (self.visited) 'V' else 'U';
std.debug.print("Elephant {u} ({u}). ", .{ self.letter, v});
}
};
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 (true) {
e.print();
e.visit();
// Get the next elephant or stop.
if (e.hasTail()) {
e = e.???; // Which method do we want here?
} else {
break;
}
}
}
// Bonus: Zig's enums can also have methods! Can you find
// one in the wild? If you can, mention it along with your
// name or alias in a comment below this one and make a
// pull request on GitHub for a piece of eternal Ziglings
// glory. The first five (5) PRs will be accepted!

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@ -1,8 +1,21 @@
12c12
< tail: *Elephant = null, // <---- make this optional!
8,19d7
< // 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!
< //
24c12
< tail: *Elephant = null, // Hmm... tail needs something...
---
> tail: ?*Elephant = null, // <---- make this optional!
42c42
54c42
< if (e.tail == null) ???;
---
> if (e.tail == null) break;

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@ -0,0 +1,4 @@
57c57
< e = e.???; // Which method do we want here?
---
> e = e.getTail(); // Which method do we want here?