Mutable Global Data in Zig

#learn

Sometimes you want to write a small test file, or some example code, that shows how to mutate a string or slice of data.

But how do you make a global mutable var prefilled with example data?

The recipe is:

make a const array of the example data
make a var that copies that data

const std = @import("std");

// strings
const data_str = "hello";
var mut_str = data_str.*; // deref string to get array

// struct arrays
const foo = struct {
    ord: enum { first, second },
};
const data_foo = [_]foo{ .{ .ord = .first }, .{ .ord = .second } };
var mut_foo = data_foo;

pub fn main() !void {

    // upcase string
    for (0..mut_str.len) |i| {
        mut_str[i] = std.ascii.toUpper(mut_str[i]);
    }

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

    // swap foos
    const temp = mut_foo[0];
    mut_foo[0] = mut_foo[1];
    mut_foo[1] = temp;

    for (mut_foo, 0..) |f, i| {
        std.debug.print("foo[{d}]: {s}\n", .{ i, @tagName(f.ord) });
    }
}