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update ch04-01 close #682

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KaiserY 2023-01-18 22:10:25 +08:00
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src/ch04-01-what-is-ownership.md
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@ -143,15 +143,17 @@ style="width: 50%;" />
当我们将 `s1` 赋值给 `s2`，`String` 的数据被复制了，这意味着我们从栈上拷贝了它的指针、长度和容量。我们并没有复制指针指向的堆上数据。换句话说，内存中数据的表现如图 4-2 所示。
<img alt="s1 and s2 pointing to the same value" src="img/trpl04-02.svg" class="center" style="width: 50%;" />
<img alt="Three tables: tables s1 and s2 representing those strings on the
stack, respectively, and both pointing to the same string data on the heap."
src="img/trpl04-02.svg" class="center" style="width: 50%;" />
<span class="caption">图 4-2：变量 `s2` 的内存表现，它有一份 `s1` 指针、长度和容量的拷贝</span>
这个表现形式看起来 **并不像** 图 4-3 中的那样，如果 Rust 也拷贝了堆上的数据，那么内存看起来就是这样的。如果 Rust 这么做了，那么操作 `s2 = s1` 在堆上数据比较大的时候会对运行时性能造成非常大的影响。
<img alt="Three tables: tables s1 and s2 representing those strings on the
stack, respectively, and both pointing to the same string data on the heap."
src="img/trpl04-02.svg" class="center" style="width: 50%;" />
<img alt="Four tables: two tables representing the stack data for s1 and s2,
and each points to its own copy of string data on the heap."
src="img/trpl04-03.svg" class="center" style="width: 50%;" />
<span class="caption">图 4-3：另一个 `s2 = s1` 时可能的内存表现，如果 Rust 同时也拷贝了堆上的数据的话</span>