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Added Ex 101 "for loops part 5" (Closes #271)
Also gave a shot at explaining data-oriented design, a Zig "hot topic" ever since the red Hawaiian shirt talk(s).
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@ -1076,6 +1076,10 @@ const exercises = [_]Exercise{
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.main_file = "100_for4.zig",
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.output = "Arrays match!",
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},
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.{
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.main_file = "101_for5.zig",
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.output = "1. Wizard (Gold: 25, XP: 40)\n2. Bard (Gold: 11, XP: 17)\n3. Bard (Gold: 5, XP: 55)\n4. Warrior (Gold: 7392, XP: 21)",
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},
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.{
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.main_file = "999_the_end.zig",
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.output = "\nThis is the end for now!\nWe hope you had fun and were able to learn a lot, so visit us again when the next exercises are available.",
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120
exercises/101_for5.zig
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120
exercises/101_for5.zig
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//
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// The 'for' loop is not just limited to looping over one or two
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// items. Let's try an example with a whole bunch!
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//
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// But first, there's one last thing we've avoided mentioning
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// until now: The special range that leaves off the last value:
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//
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// for ( things, 0.. ) |t, i| { ... }
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//
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// That's how we tell Zig that we want to get a numeric value for
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// every item in "things", starting with 0.
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//
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// A nice feature of these index ranges is that you can have them
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// start with any number you choose. The first value of "i" in
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// this example will be 500, then 501, 502, etc.:
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//
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// for ( things, 500.. ) |t, i| { ... }
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//
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// Remember our RPG characters? They had the following
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// properties, which we stored in a struct type:
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//
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// class
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// gold
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// experience
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//
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// What we're going to do now is store the same RPG character
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// data, but in a separate array for each property.
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//
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// It might look a little awkward, but let's bear with it.
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//
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// We've started writing a program to print a numbered list of
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// characters with each of their properties, but it needs a
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// little help:
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//
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const std = @import("std");
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const print = std.debug.print;
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// This is the same character class enum we've seen before.
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const Class = enum {
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wizard,
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thief,
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bard,
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warrior,
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};
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pub fn main() void {
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// Here are the three "property" arrays:
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const classes = [4]Class{ .wizard, .bard, .bard, .warrior };
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const gold = [4]u16{ 25, 11, 5, 7392 };
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const experience = [4]u8{ 40, 17, 55, 21 };
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// We would like to number our list starting with 1, not 0.
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// How do we do that?
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for (classes, gold, experience, ???) |c, g, e, i| {
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const class_name = switch (c) {
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.wizard => "Wizard",
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.thief => "Thief",
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.bard => "Bard",
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.warrior => "Warrior",
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};
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std.debug.print("{d}. {s} (Gold: {d}, XP: {d})\n", .{
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i,
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class_name,
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g,
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e,
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});
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}
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}
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//
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// By the way, storing our character data in arrays like this
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// isn't *just* a silly way to demonstrate multi-object 'for'
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// loops.
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//
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// It's *also* a silly way to introduce a concept called
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// "data-oriented design".
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//
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// Let's use a metaphor to build up an intuition for what this is
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// all about:
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//
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// Let's say you've been tasked with grabbing three glass
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// marbles, three spoons, and three feathers from a bucket. But
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// you can't use your hands to grab them. Instead, you have a
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// special marble scoop, spoon magnet, and feather tongs to grab
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// each type of object.
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//
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// Now, would you rather have:
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//
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// A. The items layered so you have to pick up one marble, then
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// one spoon, then one feather?
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//
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// OR
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//
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// B. The items separated by type so you can pick up all of the
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// marbles at once, then all the spoons, then all of the
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// feathers?
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//
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// If this metaphor is working, hopefully it's clear that the 'B'
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// option would be much more efficient.
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//
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// Well, it probably comes as little surprise that storing and
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// using data in a sequential and uniform fashion is also more
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// efficient for modern CPUs.
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//
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// Decades of OOP practices have steered people towards grouping
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// different data types together into "objects" with the hope
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// that it would be friendlier to the human mind. But
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// data-oriented design groups data in a way that is more
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// efficient for the computer.
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//
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// In Zig terminology, the difference in groupings is sometimes
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// known as "Array of Structs" (AoS) versus "Struct of Arrays"
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// (SoA).
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//
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// To envision these two designs in action, imagine an array of
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// RPG character structs, each containing three different data
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// types (AoS) versus a single RPG character struct containing
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// three arrays of one data type each, like those in the exercise
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// above (SoA).
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//
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4
patches/patches/101_for5.patch
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4
patches/patches/101_for5.patch
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@ -0,0 +1,4 @@
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54c54
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< for (classes, gold, experience, ???) |c, g, e, i| {
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---
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> for (classes, gold, experience, 1..) |c, g, e, i| {
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