pmalhaire

Posted on Feb 7, 2021 • Edited on Feb 12, 2021

Have you ever tried Zig ?

#ziglang #memory #safety

hello zig : explore zig through a LIFO buffer

zig has many things that are really cool :

small language : not many thing to have in brain
pointers and memory safety
multiplatform
early project everything is to be done

deps

install zig : https://ziglang.org/download/

install zig for vim : https://github.com/ziglang/zig.vim

starting over

let's say hello world :

const std = @import("std");


pub fn main() void {
    // WRONG on purpose
    std.debug.print("hello, world !\n");
}

wrong here

std.debug.print takes two arguments so the basic hello world is

const std = @import("std");


pub fn main() void {
    std.debug.print("hello, world !\n", .{});
}

It looks strange at first but why not.

There we can see that zig is not a hype language : From the first function choices have been made.

doc generation

Not ready yet.

Auto doc is underway see : https://github.com/tiehuis/zig-docgen

doing a basic io/buffer

let's try zig with a simple async io/buffer.

goal is write / read async char by char.

step 1 alloc

what we need :

store data

struct : https://ziglang.org/documentation/master/#struct

allocator

memory : https://ziglang.org/documentation/master/#memory

Note : At first you may want to use pointer arithmetics. But slices are forced by the language no pointer arithmetics !

https://github.com/ziglang/zig/issues/45

slices

Slice follow a very similar syntax than golang one :

// write a slice
const slice: []const u8 = "hello slice";
// write an array
const array: [11]u8 = "hello array".*;

see : https://ziglang.org/documentation/master/#Slices

test alloc sample

It's where zig doc must be read.

and make a small alloc sample

alloc a slice
write slice
free slice

here zig has a nice test feature :
let's use it. see https://ziglang.org/documentation/master/#Zig-Test

const std = @import("std");
const Allocator = std.mem.Allocator;
const Gpa = std.heap.GeneralPurposeAllocator;

test "try to allocate memory" {
    // create a general pupose allocator
    var gpa = Gpa(.{ .enable_memory_limit = true }){};
    // get a reference the instance of the allocator
    var allocator = &gpa.allocator;
    // check that no memory has been requested
    std.testing.expect(gpa.total_requested_bytes == 0);

    // allocate some memory (not the try)
    const ptr = try allocator.alloc(u8,10);

    // check that the allocation success
    std.testing.expect(gpa.total_requested_bytes == 10);

    // free memory
    allocator.free(ptr);

    // check free success
    std.testing.expect(gpa.total_requested_bytes == 0);

}

run the test

zig test alloc.zig

step 2 :sync lifo

Now that the allocation is cleared. Let's now get back to our buffer.

Many zig function use the maybe concept.
Coming fron the Maybe monad in Haskell then adapted to other languages.
For example the std:optionnal in cpp.

This tells that a function either succeed or returns an error :
ErrorType!ReturnType

This is a very elegant way of handling error and avoid other language issues :

If error checks of golang (improved since 1.13).
Exception handling in python (not improved here).

see https://ziglang.org/documentation/master/#Errors

code

We write 4 functions :

init

fn init(size: u32, a: *Allocator) Error!*Buff {

write

fn write(b: *Buff, c: u8) void {

read

fn read(b: *Buff) u8 {

fn close(b: *Buff) void {

The program :

const std = @import("std");
const Allocator = std.mem.Allocator;
const GPA = std.heap.GeneralPurposeAllocator;
const Error = std.mem.Allocator.Error;

/// Buff struct
/// size the size of the buffer
/// addr the address of the undelying memory block
/// offset the first unused place in the buffer 0xffff means the buff is full
/// allocator the address of the us allocator
const Buff = struct {
    size: u32,
    addr: []u8,
    offset: u32,
    allocator: *Allocator,
};

/// init a buffer of the deisred size
fn init(size: u32, a: *Allocator) Error!*Buff {

    var ptr = try a.alloc(u8, size);
    return &Buff{
        .size = size,
        .addr = ptr,
        .offset = 0,
        .allocator = a,
    };
}

/// close the given buffer and free it's memory
fn close(b: *Buff) void {
    b.allocator.free(b.addr);
}

/// write c into our buffer
fn write(b: *Buff, c: u8) void {
    // todo add fail if more than size
    b.addr[b.offset] = c;
    b.*.offset += 1;
}

/// read c into our buffer
fn read(b: *Buff) u8 {
    b.offset -= 1;
    // todo add fail if 0
    const c: u8 = b.addr[b.offset];
    return c;
}

pub fn main() !void {
    var gpa = GPA(.{}){};
    var alloc = &gpa.allocator;

    var buff = try init(3, alloc);
    defer close(buff);

    std.debug.print("writing 'a' to buff\n", .{});
    write(buff, 'a');


    std.debug.print("reading one char from buff\n", .{});
    const c = read(buff);
    std.debug.print("char is : {c}\n", .{c});


    std.debug.print("writing 'a' then 'b' to buff\n", .{});
    write(buff, 'a');
    write(buff, 'b');



    std.debug.print("reading two char from buff\n", .{});
    const d = read(buff);
    const e = read(buff);
    std.debug.print("chars are : {c} {c}\n", .{d, e});

    // test failure uncomment next line : overflow
    // const f = read(buff);

    // test failure uncomment next line : out of bound
    // write(buff, '1'); write(buff, '2'); write(buff, '3'); write(buff, '4');

}

test it

zig run sync_buff.zig

output

writing 'a' to buff
reading one char from buff
char is : a
writing 'a' then 'b' to buff
reading two char from buff
chars are : b a

safety

Let's try to read a value that is not there.

uncomment the overflow error in sync_buff.zig

zig run sync_buff.zig

error :

thread 34197 panic: integer overflow
/home/pierrot/dev/helloZig/sync_buff.zig:44:14: 0x2363d1 in read (sync_buff)
    b.offset -= 1;
             ^
/home/pierrot/dev/helloZig/sync_buff.zig:78:19: 0x22ddb4 in main (sync_buff)
    const f = read(buff);
                  ^
/home/pierrot/.zig/lib/std/start.zig:345:37: 0x205684 in std.start.posixCallMainAndExit (sync_buff)
            const result = root.main() catch |err| {
                                    ^
/home/pierrot/.zig/lib/std/start.zig:163:5: 0x205522 in std.start._start (sync_buff)
    @call(.{ .modifier = .never_inline }, posixCallMainAndExit, .{});
    ^
Aborted (core dumped)

Let's try to read a value that is not there.

uncomment the out of bound error in sync_buff.zig

zig run sync_buff.zig

error :

thread 35402 panic: index out of bounds
/home/pierrot/dev/helloZig/sync_buff.zig:38:11: 0x2362a9 in write (sync_buff)
    b.addr[b.offset] = c;
          ^
/home/pierrot/dev/helloZig/sync_buff.zig:83:64: 0x22ddec in main (sync_buff)
    write(buff, '1'); write(buff, '2'); write(buff, '3'); write(buff, '4');
                                                               ^
/home/pierrot/.zig/lib/std/start.zig:345:37: 0x205684 in std.start.posixCallMainAndExit (sync_buff)
            const result = root.main() catch |err| {
                                    ^
/home/pierrot/.zig/lib/std/start.zig:163:5: 0x205522 in std.start._start (sync_buff)
    @call(.{ .modifier = .never_inline }, posixCallMainAndExit, .{});
    ^
Aborted (core dumped)

samples

All code samples here are available in this repo : https://github.com/pmalhaire/helloZig.

Conclusion

Zig is definetly simple for an experienced developper. It exposes in a simple maner complex concepts.
It's a very good language to have in your toolbox. It will probably grow fast in the coming years.

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