A simple UUID v4 Generator

main.zig

const std = @import("std");
const stdout = std.io.getStdOut().writer();

pub fn hasArguments() !bool {
    var general_purpose_allocator = std.heap.GeneralPurposeAllocator(.{}){};
    const gpa = &general_purpose_allocator.allocator;
    const args = try std.process.argsAlloc(gpa);
    defer std.process.argsFree(gpa, args);

    return args.len > 1;
}

const UUID = struct {
    uuid: [16]u8 = [16]u8{ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 },
    pub fn new() UUID {
        var u = UUID{};
        std.crypto.random.bytes(u.uuid[0..]);
        u.uuid[6] = (u.uuid[6] & 0b00001111) | 0b01000000;
        return u;
    }

    const zero = UUID{};

    pub fn str(u: UUID, buf: *[36] u8) void {
        const charset = "0123456789abcdef";

        var j: u8 = 0;
        for (u.uuid) |c, i| {
            if (i == 4 or i == 6 or i == 8 or i == 10) {
                buf[j] = '-';
                j += 1;
            }

            buf[j] = charset[c >> 4];
            buf[j + 1] = charset[c & 15];
            j += 2;
        }
    }

    pub fn newstr(u: UUID) [36]u8 {
        var buf: [36]u8 = undefined;
        u.str(&buf);
        return buf;
    }
};

pub fn main() !void {
    var args = try hasArguments();

    const u = if (args) UUID.zero else UUID.new();

    _ = try stdout.write(u.newstr()[0..]);
}

Makefile

uuid: main.zig
	zig build-exe --strip --single-threaded main.zig
	mv main uuid

run: uuid
	./uuid

uuid.zig

const std = @import("std");

const chars: []const u8 = "0123456789ABCDEF";

pub const UUID = struct {
    const Self = @This();
    id: [36]u8,

    pub fn new(seed: u64) !*Self {
        var r = std.rand.DefaultPrng.init(seed);
        var uu = try std.heap.page_allocator.create(Self);

        var i: usize = 0;
        while (i < 36) : (i += 1) {
            uu.id[i] = '0';
        }

        uu.id[8] = '-';
        uu.id[13] = '-';
        uu.id[14] = '4';
        uu.id[18] = '-';
        uu.id[23] = '-';

        i = 0;
        while (i < 36) : (i += 1) {
            if (i != 8 and i != 13 and i != 14 and i != 18 and i != 23) {
                var res: u8 = r.random.uintLessThanBiased(u8, 16);
                uu.id[i] = chars[res];
            }
        }

        return uu;
    }
};