Add ex 47: methods

This commit is contained in:
Dave Gauer 2021-02-27 16:52:57 -05:00
parent d2b4e7a87b
commit 42e6ebd2fe
3 changed files with 105 additions and 3 deletions

View file

@ -40,7 +40,7 @@ const exercises = [_]Exercise{
.{
.main_file = "01_hello.zig",
.output = "Hello world",
.hint = "Note the error: the source file has a hint for fixing 'main'.",
.hint = "DON'T PANIC!\nRead the error above.\nSee how it has something to do with 'main'?\nOpen up the source file as noted and read the comments.\nYou can do this!",
},
.{
.main_file = "02_std.zig",
@ -243,9 +243,13 @@ const exercises = [_]Exercise{
.{
.main_file = "46_optionals2.zig",
.output = "Elephant A. Elephant B. Elephant C.",
.hint = "Elephants!",
.hint = "Elephants again!",
},
.{
.main_file = "47_methods.zig",
.output = "5 aliens. 4 aliens. 1 aliens. 0 aliens. Earth is saved!",
.hint = "Use the heat ray. And the method!",
},
// super-simple struct method
// use struct method for elephant tails
// quiz: add elephant trunk (like tail)!
};

94
exercises/47_methods.zig Normal file
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@ -0,0 +1,94 @@
//
// Help! Evil alien creatures have hidden eggs all over the Earth
// and they're starting to hatch!
//
// Before you jump into battle, you'll need to know four things:
//
// 1. You can attach functions to structs:
//
// const Foo = struct{
// pub fn hello() void {
// std.debug.print("Foo says hello!\n", .{});
// }
// }
//
// 2. A function that is a member of a struct is a "method" and is
// called with the "dot syntax" like so:
//
// Foo.hello();
//
// 3. The NEAT feature of methods is the special parameter named
// "self" that takes an instance of that type of struct:
//
// const Bar = struct{
// number: u32,
//
// pub fn printMe(self: *Bar) void {
// std.debug.print("{}\n", .{self.number});
// }
// }
//
// 4. Now when you call the method on an INSTANCE of that struct
// with the "dot syntax", the instance will be automatically
// passed as the "self" parameter:
//
// const my_bar = Bar{ .number = 2000 };
// my_bar.printMe(); // prints "2000"
//
// Okay, you're armed.
//
// Now, please zap the alien structs until they're all gone or
// Earth will be doomed!
//
const std = @import("std");
// Look at this hideous Alien struct. Know your enemy!
const Alien = struct {
health: u8,
// We hate this method:
pub fn hatch(strength: u8) Alien {
return Alien{
.health = strength * 5,
};
}
// We love this method:
pub fn zap(self: *Alien, damage: u8) void {
self.health -= if (damage >= self.health) self.health else damage;
}
};
pub fn main() void {
// Look at all of these aliens of various strengths!
var aliens = [_]Alien{
Alien.hatch(2),
Alien.hatch(1),
Alien.hatch(3),
Alien.hatch(3),
Alien.hatch(5),
Alien.hatch(3),
};
var aliens_alive = aliens.len;
var heat_ray_strength: u8 = 7; // We've been given a heat ray weapon.
// We'll keep checking to see if we've killed all the aliens yet.
while (aliens_alive > 0) {
aliens_alive = 0;
// Loop through every alien...
for (aliens) |*alien| {
// *** Zap the Alien Here! ***
???.zap(heat_ray_strength);
// If the alien's health is still above 0, it's still alive.
if (alien.health > 0) aliens_alive += 1;
}
std.debug.print("{} aliens. ", .{aliens_alive});
}
std.debug.print("Earth is saved!\n", .{});
}

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@ -0,0 +1,4 @@
84c84
< ???.zap(heat_ray_strength);
---
> alien.zap(heat_ray_strength);