小编alx*_*olm的帖子

我想做这个:

struct Point {
    x: i32,
    y: i32,
}

impl Point {
    fn up(&self) {
        self.y += 1;
    }
}

fn main() {
    let p = Point { x: 0, y: 0 };
    p.up();
}

但是这段代码抛出了编译器错误:

error[E0594]: cannot assign to field `self.y` of immutable binding
 --> src/main.rs:8:9
  |
7 |     fn up(&self) {
  |           ----- use `&mut self` here to make mutable
8 |         self.y += 1;
  |         ^^^^^^^^^^^ cannot mutably borrow field of immutable binding

我在Haskell中有这个代码:

import Control.Monad.Trans.State

simpleState = state (\x -> (x, x + 1))

runUntil :: (s -> Bool) -> State s a -> State s a
runUntil f s = do
    s' <- get
    -- Here I want to print value of s' to console
    if f s'
        then s >> runUntil f s
        else s

main :: IO ()
main = do
    let (x,s) = runState (runUntil (< 10) simpleState) 0
    putStrLn $ "State = " ++ (show s) ++ …

我有解决c-union结构XEvent的问题.

我在Rust中试验Xlib和X Record Extension.我用rust-bindgen生成ffi-bindings .所有代码都托管在github alxkolm/rust-xlib-record上.

当我尝试从XEvent结构中提取数据时,在src/main.rs:106行发生了故障.

let key_event: *mut xlib::XKeyEvent = event.xkey();
println!("KeyPress {}", (*key_event).keycode); // this always print 128 on any key

我的程序听取关键事件并打印出来keycode.但是我按下的任何按键总是128.我认为从C union类型到Rust类型的这种错误转换.

XEvent的定义从这里开始src/xlib.rs:1143.这是c-union.原始C定义在这里.

GitHub中的代码可以通过cargo run命令运行.它编译没有错误.

我做错了什么？