Heap allocated struct with default null value Segfaults

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8

My favorite way of doing initialization is to have 2 “constructors”, one for stack allocation and the other one for heap allocation. Using your linked list example it would be something like this:

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

const Node = packed struct {
    value: i32,
    next: ?*Node = null,

    fn init(val: i32) Node {
        return .{.value = val};
    }

    fn create(val: i32, a: Allocator) !*Node {
        const np = try a.create(Node);
        np.* = init(val);;
        return np;
    }
};

fn printNodes(n: *const Node) void {
    var maybe_node: ?*const Node = n;
    while (maybe_node) |node| {
        std.debug.print("node.value {d}\n", .{node.value});
        std.debug.print("node 0x{x:0>24}\n", .{@as(u96, @bitCast(node.*))});
        maybe_node = node.next;
    }
}

pub fn main() !void {

    const stackNode =  Node.init(1);
    printNodes(&stackNode);

    var gpa = std.heap.GeneralPurposeAllocator(.{}){};
    defer _ = gpa.deinit();
    var allocator = gpa.allocator();

    const heapNode = try Node.create(2, allocator);
    defer allocator.destroy(heapNode);
    printNodes(heapNode);
}
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