ziglings/exercises/048_methods2.zig

//
// Now that we've seen how methods work, let's see if we can help
// our elephants out a bit more with some Elephant methods.
//
const std = @import("std");

const Elephant = struct {
    letter: u8,
    tail: ?*Elephant = null,
    visited: bool = false,

    // New Elephant methods!
    pub fn getTail(self: *Elephant) *Elephant {
        return self.tail.?; // Remember, this means "orelse unreachable"
    }

    pub fn hasTail(self: *Elephant) bool {
        return (self.tail != null);
    }

    pub fn visit(self: *Elephant) void {
        self.visited = true;
    }

    pub fn print(self: *Elephant) void {
        // Prints elephant letter and [v]isited
        const v: u8 = if (self.visited) 'v' else ' ';
        std.debug.print("{u}{u} ", .{ self.letter, v });
    }
};

pub fn main() void {
    var elephantA = Elephant{ .letter = 'A' };
    var elephantB = Elephant{ .letter = 'B' };
    var elephantC = Elephant{ .letter = 'C' };

    // This links the elephants so that each tail "points" to the next.
    elephantA.tail = &elephantB;
    elephantB.tail = &elephantC;

    visitElephants(&elephantA);

    std.debug.print("\n", .{});
}

// This function visits all elephants once, starting with the
// first elephant and following the tails to the next elephant.
fn visitElephants(first_elephant: *Elephant) void {
    var e = first_elephant;

    while (true) {
        e.print();
        e.visit();

        // This gets the next elephant or stops:
        // which method do we want here?
        e = if (e.hasTail()) e.??? else break;
    }
}

// Zig's enums can also have methods! This comment originally asked
// if anyone could find instances of enum methods in the wild. The
// first five pull requests were accepted and here they are:
//
// 1) drforester - I found one in the Zig source:
// https://github.com/ziglang/zig/blob/041212a41cfaf029dc3eb9740467b721c76f406c/src/Compilation.zig#L2495
//
// 2) bbuccianti - I found one!
// https://github.com/ziglang/zig/blob/6787f163eb6db2b8b89c2ea6cb51d63606487e12/lib/std/debug.zig#L477
//
// 3) GoldsteinE - Found many, here's one
// https://github.com/ziglang/zig/blob/ce14bc7176f9e441064ffdde2d85e35fd78977f2/lib/std/target.zig#L65
//
// 4) SpencerCDixon - Love this language so far :-)
// https://github.com/ziglang/zig/blob/a502c160cd51ce3de80b3be945245b7a91967a85/src/zir.zig#L530
//
// 5) tomkun - here's another enum method
// https://github.com/ziglang/zig/blob/4ca1f4ec2e3ae1a08295bc6ed03c235cb7700ab9/src/codegen/aarch64.zig#L24