FooBar

const std = @import("std");

const Foo = struct {
    const Self = @This();
    bar:std.ArrayList(u8) = undefined,

    pub fn init(allocator: std.mem.Allocator) Foo {
        var bar = std.ArrayList(u8).init(allocator);
        return .{ .bar = bar };
    }

    pub fn deinit(self: Self) void {
        self.bar.deinit();
    }
};

pub fn main() !void {
    var gpa = std.heap.GeneralPurposeAllocator(.{}){};
    const allocator = gpa.allocator();

    var foo = Foo.init(allocator);
    defer foo.deinit();

    std.debug.print("Hello, World! {}\n", .{foo.bar});
    try foo.bar.append(10);
    std.debug.print("Hello, World! {}\n", .{foo.bar});
}

To print a nice array

    std.debug.print("Hello, World! {any}\n", .{foo.bar.items});
    try foo.bar.append(10);
    std.debug.print("Hello, World! {any}\n", .{foo.bar.items});