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//
// 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 three things:
//
// 1. You can attach functions to structs (and other "type definitions"):
//
// 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 "namespaced" within
// that struct and is called by specifying the "namespace" and then
// using the "dot syntax":
//
// Foo.hello();
//
// 3. The NEAT feature of these functions is that if their first argument
// is an instance of the struct (or a pointer to one) then we can use
// the instance as the namespace instead of the type:
//
// const Bar = struct{
// pub fn a(self: Bar) void {}
// pub fn b(this: *Bar, other: u8) void {}
// pub fn c(bar: *const Bar) void {}
// };
//
// var bar = Bar{};
// bar.a() // is equivalent to Bar.a(bar)
// bar.b(3) // is equivalent to Bar.b(&bar, 3)
// bar.c() // is equivalent to Bar.c(&bar)
//
// Notice that the name of the parameter doesn't matter. Some use
// self, others use a lowercase version of the type name, but feel
// free to use whatever is most appropriate.
//
// 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,
};
}
};
// Your trusty weapon. Zap those aliens!
const HeatRay = struct {
damage: u8,
// We love this method:
pub fn zap(self: HeatRay, alien: *Alien) void {
alien.health -= if (self.damage >= alien.health) alien.health else self.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;
const heat_ray = HeatRay{ .damage = 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 by reference (* makes a pointer capture value)
for (&aliens) |*alien| {
// *** Zap the alien with the heat ray here! ***
???.zap(???);
// 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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