Confusion related to zig pointers and structs

struct_repro.zig

const std = @import("std");

// zig version: 0.11.0-dev.2249+dcdb87836

/////////////////////////////////////////////
// zig run -O Debug struct_repro.zig

// rand 1 0.47344332933425903
// rand 1 0.3766399025917053
// rand 2 0.6770572662353516
// rand 2 0.5922629833221436
// rand 3 0.8293377757072449
// rand 3 0.5863988399505615
// rand 4 0.6468727588653564
// rand 4 0.18700581789016724
// [1]    67389 abort      zig run -O Debug struct_repro.zig

///////////////////////////////////////////////

// zig run -O ReleaseSafe struct_repro.zig

// rand 1 0.6165003180503845
// rand 1 0.09705868363380432
// rand 2 0.2942855656147003
// rand 2 0.3366544246673584
// rand 3 0.0039062497671693563
// rand 3 0.00000000118555465444814
// rand 4 0.900171160697937
// rand 4 0.3476182520389557
// rand 5 0.978439450263977
// rand 5 0.04816720262169838

///////////////////////////////////////////////

// zig run -O ReleaseFast struct_repro.zig

// rand 1 0.07979004830121994
// rand 1 0.5140153765678406
// rand 2 0.5294123888015747
// rand 2 0.6598545908927917
// rand 3 0
// rand 3 0
// rand 4 0
// rand 4 0
// rand 5 0
// rand 5 0

const RNG = struct {
    rand: std.rand.Random,

    pub fn init() !RNG {
        var prng = std.rand.DefaultPrng.init(blk: {
            var seed: u64 = undefined;
            try std.os.getrandom(std.mem.asBytes(&seed));
            break :blk seed;
        });
        const rand = prng.random();

        return RNG{ .rand = rand };
    }

    pub fn next(self: *RNG) f32 {
        return self.rand.float(f32);
    }
};

fn rand_double1(rand: std.rand.Random) f32 {
    return rand.float(f32);
}

fn rand_double2(rng: *RNG) f32 {
    return rng.rand.float(f32);
}

fn rand_double3(rng: *RNG) f32 {
    return rng.next() * 2;
}

pub fn main() !void {
    var prng = std.rand.DefaultPrng.init(blk: {
        var seed: u64 = undefined;
        try std.os.getrandom(std.mem.asBytes(&seed));
        break :blk seed;
    });
    const rand = prng.random();

    // calling float directly works
    std.debug.print("rand 1 {d} \n", .{rand.float(f32)});
    std.debug.print("rand 1 {d} \n", .{rand.float(f32)});

    // passing rand to function works
    std.debug.print("rand 2 {d} \n", .{rand_double1(rand)});
    std.debug.print("rand 2 {d} \n", .{rand_double1(rand)});

    // pass the rng wrapper to a function
    var rng = try RNG.init();
    std.debug.print("rand 3 {d} \n", .{rand_double2(&rng)});
    std.debug.print("rand 3 {d} \n", .{rand_double2(&rng)});

    // use next fn
    std.debug.print("rand 4 {d} \n", .{rng.next()});
    std.debug.print("rand 4 {d} \n", .{rng.next()});

    // pass to rng to function
    std.debug.print("rand 5 {d} \n", .{rand_double3(&rng)});
    std.debug.print("rand 5 {d} \n", .{rand_double3(&rng)});
}