RWops does not live long enough

[Flaise]

I'm trying to store a mixer::Music instance in a data structure for later retrieval. The data structure expects its contents to have the 'static lifetime because it uses standard library functions like TypeId::of and such that require it. I'm having trouble making it work.

extern crate sdl2;

use std::thread::sleep;
use std::time::Duration;
use sdl2::mixer::{self, LoaderRWops, INIT_OGG, open_audio, allocate_channels, AUDIO_S16LSB, Music};
use sdl2::rwops::RWops;

// I can't omit the 'static constraint because I use standard library functions that require it.
pub trait Data: 'static {
    // details elided
}

pub fn set_data<D: Data>(element: D) {
    // details elided
}

struct MusicData<'a> {
    music: Music<'a>,
    buffer: RWops<'a>,
}

impl Data for MusicData<'static> {}

pub fn init_music(bytes: &'static [u8]) {
    let buffer = RWops::from_bytes(bytes).unwrap();
    let music = buffer.load_music().unwrap();
    set_data(MusicData {music, buffer});
}

fn main() {
    let context = mixer::init(INIT_OGG).unwrap();

    let frequency = 44100;
    let format = AUDIO_S16LSB;
    let channels = 2;
    let chunk_a_size = 1024;
    open_audio(frequency, format, channels, chunk_a_size).unwrap();
    allocate_channels(100);

    init_music(include_bytes!("./test_music.ogg"));

    sleep(Duration::from_secs(10));
}

The compiler gives this error:

error[E0597]: `buffer` does not live long enough
  --> src/bin/test_music.rs:26:17
   |
26 |     let music = buffer.load_music().unwrap();
   |                 ^^^^^^ does not live long enough
27 |     set_data(MusicData {music, buffer});
28 | }
   | - borrowed value only lives until here
   |
   = note: borrowed value must be valid for the static lifetime...

You'll notice that init_music already stipulates that the original source of its data lives for the 'static lifetime and the implementation of the Music and RWops structs look to me like they should take the same lifetime as bytes. The lifetime parameter of MusicData is supposed to specify that buffer lives as long as music. But that's not what the compiler is saying. I'm confused. Can you help?

[Cobrand]

Try to remove your init_music function and put it in he main, and tell me how it goes. It looks like this is more of a Rust lifetime problem than an SDL2 problem.

For questions like this, I'd advise you to ask #rust or #rust-beginners, they will be able to help you much faster than I do :)

[Flaise]

Putting it directly in main() doesn't work - it gives basically the same error.

I spoke with someone on the #rust channel and he explained more about how lifetimes work. Apparently lifetimes aren't transitive like I thought. If the contents of a RWops object has the 'static lifetime, that only means the RWops has itself a lifetime that is not longer than 'static. In this case, it still has a shorter lifetime because its drop() function is called whenever the containing data structure is dropped.

What I need is a Music<'static> instance, which I can get when I use Music::from_file() but what I'm looking for is a way to do it with a &'static [u8]. Is that something that can be done?

[Flaise]

Solved by #704.

[Flaise]

Any idea when #704 will be published to crates.io?

[Cobrand]

I've got 2 PRs to merge before that, I'm planning to do it this week end or at the latest next week end.

…

On Sep 21, 2017, 17:38, at 17:38, Flaise ***@***.***> wrote: Any idea when #704 will be published to crates.io? -- You are receiving this because you commented. Reply to this email directly or view it on GitHub: #696 (comment)