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https://github.com/anonymousGiga/Rustonomicon-Source

详细内容

drain 是一个集合 API，它将容器内的数据所有权移出，却不占有容器本身。我们可以声明一个 Vec 所有内容的所有权，然后复用分配给它的空间。它产生一个迭代器（Drain），以返回 Vec 的所有值。

代码如下：

#![feature(ptr_internals)]
use std::mem;
use std::alloc::{alloc, realloc, dealloc, Layout, handle_alloc_error};
use std::ptr::{Unique, self};
use std::ops::{Deref, DerefMut};
use std::slice;#[derive(Debug)]
struct RawVec<T> {ptr: Unique<T>,cap: usize,
}impl<T> RawVec<T> {fn new() -> Self {assert!(mem::size_of::<T>() != 0, "还没准备好处理零尺寸类型");RawVec { ptr: Unique::dangling(), 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;}}
}impl<T> Drop for RawVec<T> {fn drop(&mut self) {if self.cap != 0 {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!");}}
}struct IntoIter<T> {_buf: RawVec<T>, iter: RawValIter<T>,
}impl<T> Drop for IntoIter<T> {fn drop(&mut self) {for _ in &mut *self {}}
}#[derive(Debug)]
pub struct MyVec<T> {buf: RawVec<T>,len: usize,
}impl<T> MyVec<T> {fn ptr(&self) -> *mut T { self.buf.ptr.as_ptr() }fn cap(&self) -> usize { self.buf.cap }pub fn new() -> Self {MyVec { buf: RawVec::new(), len: 0 }}fn push(&mut self, elem: T) {if self.len == self.cap() { self.buf.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().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().offset(self.len as isize)))}}}fn insert(&mut self, index: usize, elem: T) {assert!(index <= self.len, "越界");if self.cap() == self.len { self.buf.grow(); }unsafe {if index < self.len {ptr::copy(self.ptr().offset(index as isize),self.ptr().offset((index as isize) + 1),self.len - index);}ptr::write(self.ptr().offset(index as isize), elem);self.len += 1;}}fn remove(&mut self, index: usize) -> T {assert!(index < self.len, "越界");unsafe {self.len -= 1;let result = ptr::read(self.ptr().offset(index as isize));ptr::copy(self.ptr().offset(index as isize + 1), self.ptr().offset(index as isize),self.len - index);result}}fn into_iter(self) -> IntoIter<T> {unsafe {let iter = RawValIter::new(&self);let buf = ptr::read(&self.buf);mem::forget(self);IntoIter {iter: iter,_buf: buf,}}}
}impl<T> Drop for MyVec<T> {fn drop(&mut self) {while let Some(_) = self.pop() {}}
}impl<T> Deref for MyVec<T> {type Target = [T];fn deref(&self) -> &[T] {unsafe {slice::from_raw_parts(self.buf.ptr.as_ptr(), self.len)}}
}impl<T> DerefMut for MyVec<T> {fn deref_mut(&mut self) -> &mut [T] {unsafe {slice::from_raw_parts_mut(self.buf.ptr.as_ptr(), self.len)}}
}//为IntoIter实现迭代器
impl<T> Iterator for IntoIter<T> {type Item = T;fn next(&mut self) -> Option<T> {self.iter.next()}fn size_hint(&self) -> (usize, Option<usize>) {self.iter.size_hint()}
}impl<T> DoubleEndedIterator for IntoIter<T> {fn next_back(&mut self) -> Option<T> {self.iter.next_back()}
}struct RawValIter<T> {start: *const T,end: *const T,
}impl<T> RawValIter<T> {unsafe fn new(slice: &[T]) -> Self {RawValIter {start: slice.as_ptr(),end: if slice.len() == 0 {slice.as_ptr()} else {slice.as_ptr().offset(slice.len() as isize)}}}
}impl<T> Iterator for RawValIter<T> {type Item = T;fn next(&mut self) -> Option<T> {if self.start == self.end {None} else {unsafe {let result = ptr::read(self.start);self.start = self.start.offset(1);Some(result)}}}fn size_hint(&self) -> (usize, Option<usize>) {let len = (self.end as usize - self.start as usize) / mem::size_of::<T>();(len, Some(len))}
}impl<T> DoubleEndedIterator for RawValIter<T> {fn next_back(&mut self) -> Option<T> {if self.start == self.end {None} else {unsafe {self.end = self.end.offset(-1);Some(ptr::read(self.end))}}}
}use std::marker::PhantomData;
//Drain是一个API集合，将容器内数据的所有权移出，却不占有容器本身
struct Drain<'a, T: 'a> {vec: PhantomData<&'a mut MyVec<T>>,iter: RawValIter<T>,
}impl<'a, T> Iterator for Drain<'a, T> {type Item = T;fn next(&mut self) -> Option<T> { self.iter.next() }fn size_hint(&self) -> (usize, Option<usize>) {self.iter.size_hint()}
}impl<'a, T> DoubleEndedIterator for Drain<'a, T> {fn next_back(&mut self) -> Option<T> { self.iter.next_back() }
}impl<'a, T> Drop for Drain<'a, T> {fn drop(&mut self) {for _ in &mut self.iter {}}
}impl<T> MyVec<T> {fn drain(&mut self) -> Drain<T> {unsafe {let iter = RawValIter::new(&self);self.len = 0;Drain {iter: iter,vec: PhantomData,}}}
}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);}vec.push(8);vec.push(7);vec.push(6);let s = &vec[1..];println!("s[0] == {}", s[0]);let s = &mut vec[1..];s[0] = 10;println!("s[0] == {}", s[0]);println!("-------------------------------");let mut vec2: MyVec<i32> = MyVec::new();vec2.push(1);vec2.push(2);vec2.push(3);//打印//while let Some(v) = vec2.pop() {// println!("v == {}", v);//}vec2.insert(1, 11);let ret = vec2.remove(2);println!("remove elem: {}", ret);//打印while let Some(v) = vec2.pop() {println!("v == {}", v);}println!("-------------------------------");let mut vec3: MyVec<i32> = MyVec::new();vec3.push(1);vec3.push(2);vec3.push(3);vec3.push(4);let iter = vec3.iter();for val in iter {println!("Got: {}", val);}println!("-------------------------------");let iter3: IntoIter<i32> = vec3.into_iter();for mut val in iter3 {println!("Got: {}", val);val = 111;println!("Got: {}", val);}println!("-------------------------------");let mut vec4: MyVec<i32> = MyVec::new();vec4.push(1);vec4.push(2);let mut iter4: IntoIter<i32> = vec4.into_iter();while let Some(val) = iter4.next_back() {println!("Got: {}", val);}println!("-------------------------------");let mut vec5: MyVec<i32> = MyVec::new();vec5.push(11);vec5.push(12);vec5.push(13);vec5.push(14);let mut drain = vec5.drain();let a = drain.next().unwrap();println!("drain: {}", a);//从下面的打印可以看出已经借用了第一个元素while let Some(val) = drain.next_back() {println!("Got: {}", val);}}println!("Hello, world!");
}

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