Add ex 47: methods

build.zig

@@ -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)!
 };

exercises/47_methods.zig

@@ -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", .{});
+}

patches/patches/47_methods.patch

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