Added ex 45 optionals

(And secretly added the patches/ dir. Don't tell anybody!)
This commit is contained in:
Dave Gauer 2021-02-14 10:49:09 -05:00
parent 16dbeea7f5
commit 545573fc84
5 changed files with 74 additions and 0 deletions

1
.gitignore vendored
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@ -1,3 +1,4 @@
*~ *~
*.swp *.swp
zig-cache/ zig-cache/
answers/

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@ -236,6 +236,14 @@ const exercises = [_]Exercise{
.output = "Elephant A. Elephant B. Elephant C.", .output = "Elephant A. Elephant B. Elephant C.",
.hint = "Oh no! We forgot Elephant B!", .hint = "Oh no! We forgot Elephant B!",
}, },
.{
.main_file = "45_optionals.zig",
.output = "The Ultimate Answer: 42.",
},
// optional fields (elephant tail - no longer need circular)
// super-simple struct method
// use struct method for elephant tails
// quiz: add elephant trunk (like tail)!
}; };
/// Check the zig version to make sure it can compile the examples properly. /// Check the zig version to make sure it can compile the examples properly.

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@ -0,0 +1,52 @@
//
// Sometimes you know that a variable might hold a value or
// it might not. Zig has a neat way of expressing this idea
// called Optionals. An optional type just has a '?' like this:
//
// var foo: ?u32 = 10;
//
// Now foo can store a u32 integer OR null (a value storing
// the cosmic horror of a value NOT EXISTING!)
//
// foo = null;
//
// if (foo == null) beginScreaming();
//
// Before we can use the optional value as the non-null type
// (a u32 integer in this case), we need to guarantee that it
// isn't null. One way to do this is to THREATEN IT with the
// "orelse" statement.
//
// var bar = foo orelse 2;
//
// Here, bar will either equal the u32 integer value stored in
// foo, or it will equal 2 if foo was null.
//
const std = @import("std");
pub fn main() void {
const result = deepThought();
// Please threaten the result so that answer is either the
// integer value from deepThought() OR the number 42:
var answer: u8 = result;
std.debug.print("The Ultimate Answer: {}.\n",.{answer});
}
fn deepThought() ?u8 {
// It seems Deep Thought's output has declined in quality.
// But we'll leave this as-is. Sorry Deep Thought.
return null;
}
//
// Blast from the past:
//
// Optionals are a lot like error union types which can either
// hold a value or an error. Likewise, the orelse statement is
// like the catch statement used to "unwrap" a value or supply
// a default value:
//
// var maybe_bad: Error!u32 = Error.Evil;
// var number: u32 = maybe_bad catch 0;
//

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32c32
< var answer: u8 = result;
---
> var answer: u8 = result orelse 42;

9
patches/README.md Normal file
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# The ziglings/patches Directory
This is how ziglings is tested.
The patches fix the broken exercises so that they work again.
No peeking! :-)
(Further tooling and explanation goes here.)