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通过例子学习Rust

20 RAII

Variables in Rust do more than just hold data in the stack, they can also own resources, e.g. Box<T> owns memory in the heap. Because Rust enforces the RAII discipline, whenever an object goes out of scope, its destructor is called and the resources owned by it are freed. This behavior shields against resource leak bugs.

fn create_box() { // Allocate an integer in the heap let _function_box = box 3i; // `_function_box` gets destroyed here, memory gets freed } fn main() { // Allocate an integer in the heap let _boxed_int = box 5i; // new (smaller) scope { // Another heap allocated integer let _short_lived_box = box 4i; // `_short_lived_box` gets destroyed here, memory gets freed } // Create lots of boxes for _ in range(0u, 1_000) { create_box(); } // `_boxed_int` gets destroyed here, memory gets freed }

Don't take my word for it, let's check using valgrind

$ 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)

You'll never have to manually free memory again or worry about memory leaks!