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+//
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+// Loop bodies are blocks, which are also expressions. We've seen
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+// how they can be used to evaluate and return values. To further
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+// expand on this concept, it turns out we can also give names to
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+// blocks by applying a 'label':
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+//
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+// my_label: { ... }
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+//
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+// Once you give a block a label, you can use 'break' to exit
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+// from that block.
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+//
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+// outer_block: { // outer block
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+// while (true) { // inner block
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+// break :outer_block;
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+// }
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+// unreachable;
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+// }
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+//
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+// As we've just learned, you can return a value using a break
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+// statement. Does that mean you can return a value from any
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+// labeled block? Yes it does!
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+//
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+// const foo = make_five: {
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+// const five = 1 + 1 + 1 + 1 + 1;
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+// break :make_five five;
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+// };
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+//
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+// Labels can also be used with loops. Being able to break out of
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+// nested loops at a specific level is one of those things that
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+// you won't use every day, but when the time comes, it's
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+// incredibly convenient. Being able to return a value from an
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+// inner loop is sometimes so handy, it almost feels like cheating
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+// (and can help you avoid creating a lot of temporary variables).
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+//
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+// const bar: u8 = two_loop: while (true) {
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+// while (true) {
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+// break :two_loop 2;
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+// }
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+// } else 0;
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+//
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+// In the above example, the break exits from the outer loop
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+// labeled "two_loop" and returns the value 2. The else clause is
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+// attached to the outer two_loop and would be evaluated if the
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+// loop somehow ended without the break having been called.
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+//
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+// Finally, you can also use block labels with the 'continue'
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+// statement:
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+//
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+// my_while: while (true) {
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+// continue :my_while;
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+// }
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+//
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+const print = @import("std").debug.print;
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+
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+// As mentioned before, we'll soon understand why these two
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+// numbers don't need explicit types. Hang in there!
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+const ingredients = 4;
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+const foods = 4;
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+
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+const Food = struct {
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+ name: []const u8,
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+ requires: [ingredients]bool,
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+};
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+
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+// Chili Macaroni Tomato Sauce Cheese
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+// ------------------------------------------------------
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+// Mac & Cheese x x
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+// Chili Mac x x
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+// Pasta x x
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+// Cheesy Chili x x
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+// ------------------------------------------------------
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+
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+const menu: [foods]Food = [_]Food{
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+ Food{
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+ .name = "Mac & Cheese",
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+ .requires = [ingredients]bool{ false, true, false, true },
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+ },
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+ Food{
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+ .name = "Chili Mac",
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+ .requires = [ingredients]bool{ true, true, false, false },
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+ },
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+ Food{
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+ .name = "Pasta",
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+ .requires = [ingredients]bool{ false, true, true, false },
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+ },
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+ Food{
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+ .name = "Cheesy Chili",
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+ .requires = [ingredients]bool{ true, false, false, true },
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+ },
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+};
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+
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+pub fn main() void {
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+ // Welcome to Cafeteria USA! Choose your favorite ingredients
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+ // and we'll produce a delicious meal.
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+ //
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+ // Cafeteria Customer Note: Not all ingredient combinations
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+ // make a meal. The default meal is macaroni and cheese.
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+ //
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+ // Software Developer Note: Hard-coding the ingredient
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+ // numbers (based on array position) will be fine for our
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+ // tiny example, but it would be downright criminal in a real
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+ // application!
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+ const wanted_ingredients = [_]u8{ 0, 3 }; // Chili, Cheese
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+
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+ // Look at each Food on the menu...
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+ var meal = food_loop: for (menu) |food| {
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+
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+ // Now look at each required ingredient for the Food...
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+ for (food.requires) |required, required_ingredient| {
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+
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+ // This ingredient isn't required, so skip it.
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+ if (!required) continue;
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+
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+ // See if the customer wanted this ingredient.
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+ // (Remember that want_it will be the index number of
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+ // the ingredient based on its position in the
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+ // required ingredient list for each food.)
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+ var found = for (wanted_ingredients) |want_it| {
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+ if (required_ingredient == want_it) break true;
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+ } else false;
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+
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+ // We did not find this required ingredient, so we
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+ // can't make this Food. Continue the outer loop.
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+ if (!found) continue :food_loop;
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+ }
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+
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+ // If we get this far, the required ingredients were all
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+ // wanted for this Food.
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+ //
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+ // Please return this Food from the loop.
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+ break;
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+ };
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+ // ^ Oops! We forgot to return Mac & Cheese as the default
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+ // Food when the requested ingredients aren't found.
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+
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+ print("Enjoy your {s}!\n", .{meal.name});
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+}
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+
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+// Challenge: You can also do away with the 'found' variable in
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+// the inner loop. See if you can figure out how to do that!
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Dave Gauer