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6b17a18893
Add the check-exercises.py tool in the new tools directory. It is used to check that the exercises are correctly formatted, printing on stderr the invalid ones and the diff in the unified format. Update the exercises that don't use the canonical zig fmt format. Update some patches that cause the generated zig file to be incorrectly formatted.
127 lines
3.9 KiB
Zig
127 lines
3.9 KiB
Zig
//
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// Remember our ant and bee simulator constructed with unions
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// back in exercises 55 and 56? There, we demonstrated that
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// unions allow us to treat different data types in a uniform
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// manner.
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//
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// One neat feature was using tagged unions to create a single
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// function to print a status for ants *or* bees by switching:
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//
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// switch (insect) {
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// .still_alive => ... // (print ant stuff)
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// .flowers_visited => ... // (print bee stuff)
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// }
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//
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// Well, that simulation was running just fine until a new insect
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// arrived in the virtual garden, a grasshopper!
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//
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// Doctor Zoraptera started to add grasshopper code to the
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// program, but then she backed away from her keyboard with an
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// angry hissing sound. She had realized that having code for
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// each insect in one place and code to print each insect in
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// another place was going to become unpleasant to maintain when
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// the simulation expanded to hundreds of different insects.
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//
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// Thankfully, Zig has another comptime feature we can use
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// to get out of this dilema called the 'inline else'.
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//
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// We can replace this redundant code:
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//
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// switch (thing) {
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// .a => |a| special(a),
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// .b => |b| normal(b),
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// .c => |c| normal(c),
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// .d => |d| normal(d),
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// .e => |e| normal(e),
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// ...
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// }
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//
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// With:
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//
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// switch (thing) {
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// .a => |a| special(a),
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// inline else |t| => normal(t),
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// }
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//
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// We can have special handling of some cases and then Zig
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// handles the rest of the matches for us.
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//
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// With this feature, you decide to make an Insect union with a
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// single uniform 'print()' function. All of the insects can
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// then be responsible for printing themselves. And Doctor
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// Zoraptera can calm down and stop gnawing on the furniture.
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//
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const std = @import("std");
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const Ant = struct {
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still_alive: bool,
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pub fn print(self: Ant) void {
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std.debug.print("Ant is {s}.\n", .{if (self.still_alive) "alive" else "dead"});
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}
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};
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const Bee = struct {
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flowers_visited: u16,
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pub fn print(self: Bee) void {
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std.debug.print("Bee visited {} flowers.\n", .{self.flowers_visited});
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}
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};
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// Here's the new grasshopper. Notice how we've also added print
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// methods to each insect.
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const Grasshopper = struct {
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distance_hopped: u16,
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pub fn print(self: Grasshopper) void {
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std.debug.print("Grasshopper hopped {} meters.\n", .{self.distance_hopped});
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}
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};
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const Insect = union(enum) {
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ant: Ant,
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bee: Bee,
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grasshopper: Grasshopper,
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// Thanks to 'inline else', we can think of this print() as
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// being an interface method. Any member of this union with
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// with a print() method can be treated uniformly by outside
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// code without needing to know any other details. Cool!
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pub fn print(self: Insect) void {
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switch (self) {
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inline else => |case| return case.print(),
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}
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}
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};
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pub fn main() !void {
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var my_insects = [_]Insect{
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Insect{ .ant = Ant{ .still_alive = true } },
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Insect{ .bee = Bee{ .flowers_visited = 17 } },
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Insect{ .grasshopper = Grasshopper{ .distance_hopped = 32 } },
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};
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std.debug.print("Daily Insect Report:\n", .{});
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for (my_insects) |insect| {
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// Almost done! We want to print() each insect with a
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// single method call here.
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???
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}
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}
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// Our print() method in the Insect union above demonstrates
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// something very similar to the object-oriented concept of an
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// abstract data type. That is, the Insect type doesn't contain
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// the underlying data, and the print() function doesn't
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// actually do the printing.
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//
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// The point of an interface is to support generic programming:
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// the ability to treat different things as if they were the
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// same to cut down on clutter and conceptual complexity.
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//
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// The Daily Insect Report doesn't need to worry about *which*
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// insects are in the report - they all print the same way via
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// the interface!
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//
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// Doctor Zoraptera loves it.
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