RAII

Rust 的变量不只是在栈中保存数据：它们也占有资源，比如 Box<T> 占有堆（heap）中的内存。Rust 强制实行 RAII（Resource Acquisition Is Initiallization，资源获取即初始化），所以任何对象在离开作用域时，它的析构函数（destructor）就被调用，然后它占有的资源就被释放。

这种行为避免了资源泄漏（resource leak），所以你再也不用手动释放内存或者担心内存泄漏（memory leak）！下面是个快速入门示例：

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当然我们可以使用 valgrind 对内存错误进行仔细检查：

$ rustc raii.rs && valgrind ./raii
==26873== Memcheck, a memory error detector
==26873== Copyright (C) 2002-2013, and GNU GPL'd, by Julian Seward et al.
==26873== Using Valgrind-3.9.0 and LibVEX; rerun with -h for copyright info
==26873== Command: ./raii
==26873==
==26873==
==26873== HEAP SUMMARY:
==26873==     in use at exit: 0 bytes in 0 blocks
==26873==   total heap usage: 1,013 allocs, 1,013 frees, 8,696 bytes allocated
==26873==
==26873== All heap blocks were freed -- no leaks are possible
==26873==
==26873== For counts of detected and suppressed errors, rerun with: -v
==26873== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 2 from 2)

完全没有泄漏！

析构函数

Rust 中的析构函数概念是通过 Drop trait 提供的。当资源离开作用域，就调用析构函数。你无需为每种类型都实现 Drop trait，只要为那些需要自己的析构函数逻辑的类型实现就可以了。

运行下列例子，看看 Drop trait 是怎样工作的。当 main 函数中的变量离开作用域，自定义的析构函数就会被调用：

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参见：

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