Learning zig: stack and dangling pointers

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hey @AndrewCodeDev, thanks for the quick reply!

So, I got some of it right - v is discarded at the end of init, so &v is a dangling pointer. But there are still things mysterious.

Here is another example:

const std = @import("std");

const Box = struct {
    value: *const u64,

    fn one(v: u64) Box {
        std.debug.print("address of parameter v {}\n", .{&v});
        return .{
            .value = &v,
        };
    }

    fn two(v: u64) Box {
        var tmp = v;
        std.debug.print("address of var tmp {}\n", .{&tmp});
        return .{
            .value = &tmp,
        };
    }
};

pub fn main() void {
    const one = Box.one(23);
    std.debug.print("box one {}\n\n", .{one});
    const two = Box.two(23);
    std.debug.print("box two {}\n", .{two});
}

resulting in:

> zig run mem.zig
address of parameter v u64@7ffe80c80188
box one mem.Box{ .value = u64@7ffe80c80198 }

address of var tmp u64@7ffe80c80190
box two mem.Box{ .value = u64@7ffe80c80190 }

So here, when I’m using the address of the parameter directly inside of the Box, it gets changed. Whereas if I copy the value to tmp and use that address, it stays the same.

So I guess the compiler is doing something clever when using the address of a parameter in a function?