从rust-xcb调用`roots`时,“活不够长”错误

我正在尝试在xcb创建的窗口中使用Cairo表面.我有一个C例子以及Rust XCB和Cairo绑定.我差不多完成了,但这个错误对我来说仍然是一个谜.

我的代码:

fn find_visual<'a>(conn: &'a xcb::Connection, visual: xcb_visualid_t) -> Option<Visualtype<'a>> {
    let setup: Setup<'a> = conn.get_setup();
    for screen in setup.roots() {
        let d_iter: DepthIterator = screen.allowed_depths();
        for depth in d_iter {
            for vis in depth.visuals() {
                if visual == vis.visual_id() {
                    println!("Found visual");
                    return Some(vis)
                }
            }
        }
    }
    None
}

我称之为:

let visual = find_visual(&conn, screen.root_visual()).unwrap();

并获得如下错误:

src/main.rs:56:19: 56:24 error: `setup` does not live long enough
src/main.rs:56     for screen in setup.roots() {
                                 ^~~~~
src/main.rs:54:97: 68:2 note: reference must be valid for the lifetime 'a as defined on the block at 54:96...
src/main.rs:54 fn find_visual<'a>(conn: &'a xcb::Connection, visual: xcb_visualid_t) -> Option<Visualtype<'a>> {
src/main.rs:55     let setup: Setup<'a> = conn.get_setup();
src/main.rs:56     for screen in setup.roots() {
src/main.rs:57         let d_iter: DepthIterator = screen.allowed_depths();
src/main.rs:58         for depth in d_iter {
src/main.rs:59             for vis in depth.visuals() {
               ...
src/main.rs:55:45: 68:2 note: ...but borrowed value is only valid for the block suffix following statement 0 at 55:44
src/main.rs:55     let setup: Setup<'a> = conn.get_setup();
src/main.rs:56     for screen in setup.roots() {
src/main.rs:57         let d_iter: DepthIterator = screen.allowed_depths();
src/main.rs:58         for depth in d_iter {
src/main.rs:59             for vis in depth.visuals() {
src/main.rs:60                 if visual == vis.visual_id() {
               ...

屏幕和深度变量的错误相同.

有人可以解释 – 为什么“设置不够长寿”?据我所知,设置将在函数返回选项时被销毁,并且可以无限制地在函数中使用.

get_setup()代码:

pub fn get_setup(&self) -> Setup {
    unsafe {

        let setup = xcb_get_setup(self.c);
        if setup.is_null() {
            panic!("NULL setup on connection")
        }
        mem::transmute(setup)
    }
}

最佳答案 看起来绑定的生命周期注释是错误的.这是根():

impl<'a> Screen<'a> {
    pub fn roots(&self) -> ScreenIterator {
        unsafe {
            xcb_setup_roots_iterator(self.ptr)
        }
    }
}

请注意,由于函数上没有注释,因此将其隐式注释为

impl<'a> Screen<'a> {
    pub fn <'b> roots(&'b self) -> ScreenIterator<'b> {
        unsafe {
            xcb_setup_roots_iterator(self.ptr)
        }
    }
}

这是错误的.返回的ScreenIterator需要使用生命周期’a来显式注释,这是底层连接的生命周期,并且XCB似乎具有这样的约定,即它所指出的所有指针都在生命周期内绑定到连接的生命周期(请参阅包装类型base :: StructPtr的注释.这意味着需要调整生成器脚本以解决这个问题.您应该对包装箱提出问题.

请求者更新:
@SebastianRedl是对的.对于返回迭代器的所有函数,问题是在xcb crate中未设置的生命周期. rust-xcb crate的下一次生命周期更改允许成功编译代码:

impl<'a> Setup<'a> {
    pub fn roots(&self) -> ScreenIterator<'a> {
        unsafe {
             xcb_setup_roots_iterator(self.ptr)
        }
    }
}

impl<'a> Depth<'a> {
    pub fn visuals(&self) -> VisualtypeIterator<'a> {
        unsafe {
            xcb_depth_visuals_iterator(self.ptr)
        }
    }
}

impl<'a> Screen<'a> {
    pub fn allowed_depths(&self) -> DepthIterator<'a> {
        unsafe {
            xcb_screen_allowed_depths_iterator(self.ptr)
        }
    }
}
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