Extra capture in for loop

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1

I am copying bytes from one array to another:

const std = @import("std");
const print = std.debug.print;

pub fn main() void {
    const s1: [3]u8 = .{1,2,3};
    var s2: [3]u8 = .{0,0,0};

    for (s1) |x, k| {
        s2[k] = x;
    }

    print("{any}\n", .{s2});
}

With zig 0.10 the program works as was intended:

$ ./c
{ 1, 2, 3 }

With zig 0.11 and 0.12 I got an error:

$ /opt/zig-0.12/zig build-exe c.zig 
c.zig:9:18: error: extra capture in for loop
    for (s1) |x, k| {
                 ^

It looks like zig 0.11/0.12 does not want to use k for indexing an array that is not in for()
What can I do with this?

2

I’d add the 0.. to declare it as an index capture:

  for (s1, 0..) |x, k| {
      s2[k] = x;
  }
1 Like
3

Ah, ok, it’s easy, thanks!

BTW, zig 0.11 has a hint:

c.zig:9:18: note: run 'zig fmt' to upgrade your code automatically

This adds missing 0.. into the for

zig 0.12 for some reason does not have this tip.

4

You can also write your loop like this, and take advantage of the compiler checking that both arrays are the same size:

    for (s1, s2) |src, *tgt| {
        tgt.* = src;
    }
7 Likes
5

zig fmt does not do anything.
zig fmt src/main.zig does someting, but does not any upgrade… only says:

src/main.zig:232:24: error: extra capture in for loop
    for (slice) |item, i| {

in 0.13

6

I think this may have been an exclusive feature of Zig v0.11 to help with migrations from v0.10.

2 Likes
7

https://ziglang.org/download/0.11.0/release-notes.html#Multi-Object-For-Loops