介绍

本系列录制的视频主要放在B站上Rust死灵书学习视频

Rust 死灵书相关的源码资料在github.com/anonymousGiga/Rustonomi...

详细内容

实现Drop最简单的就是循环调用pop方法，不过需要注意的是，当T不需要drop时，不是一定要调用drop。

下面我们来实现drop：

#![feature(ptr_internals)]
use std::mem;
use std::alloc::{alloc, realloc, dealloc, Layout, handle_alloc_error};
use std::ptr::{Unique, self};

pub struct MyVec<T> {
    ptr: Unique<T>,
    cap: usize,
    len: usize,
}

impl<T> MyVec<T> {
    fn new() -> Self {
        assert!(mem::size_of::<T>() != 0, "还没准备好处理零尺寸类型");
        MyVec { ptr: Unique::dangling(), len: 0, cap: 0 }}

    fn grow(&mut self) {
        unsafe {let align = mem::align_of::<T>();let elem_size = mem::size_of::<T>();let layout: Layout;

            let (new_cap, ptr) = if self.cap == 0 {
                layout = Layout::from_size_align_unchecked(elem_size, align);let ptr = alloc(layout);(1, ptr)} else {let new_cap = self.cap * 2;let old_num_bytes = self.cap * elem_size;

                assert!(old_num_bytes <= (isize::MAX as usize) / 2,"capacity overflow");

                let new_num_bytes = old_num_bytes * 2;
                layout = Layout::from_size_align_unchecked(new_num_bytes, align);let ptr = realloc(self.ptr.as_ptr() as *mut _,
                                      layout,
                                    new_num_bytes);(new_cap, ptr)};

            if ptr.is_null() { handle_alloc_error(layout); }

            if let Some(ptr) = Unique::new(ptr as *mut _) {
                self.ptr = ptr;} else {
                panic!("error!");}
            self.cap = new_cap;}}

    fn push(&mut self, elem: T) {if self.len == self.cap { 
            self.grow(); 
        }

        //关键点在于要直接覆盖，因为不知道内存之前是否有东西 
        unsafe {
            ptr::write(self.ptr.as_ptr().offset(self.len as isize), elem);}
        self.len += 1;}

    fn pop(&mut self) -> Option<T> {if self.len == 0 {
            None
        } else {
            self.len -= 1;
            unsafe {Some(ptr::read(self.ptr.as_ptr().offset(self.len as isize)))}}}
}

impl<T> Drop for MyVec<T> {
    fn drop(&mut self) {if self.cap != 0 {while let Some(_) = self.pop() {}let align = mem::align_of::<T>();let elem_size = mem::size_of::<T>();let num_bytes = elem_size * self.cap;

            unsafe {let layout: Layout = Layout::from_size_align_unchecked(num_bytes, align);dealloc(self.ptr.as_ptr() as *mut _, layout)}

            println!("release memory in drop function!");}}
}



fn main() {{let mut vec: MyVec<i32> = MyVec::new();
        vec.push(8);
        vec.push(7);
        vec.push(6);while let Some(v) = vec.pop() {
            println!("v == {}", v);}}

    println!("Hello, world!");
}