語言包含兩個部分： • **安全的 Rust：**可確保記憶體安全，無法觸發未定義的行為。 • **不安全的 Rust：**如果違反先決條件，便可能觸發未定義的行為。 We saw mostly safe Rust in this course, but it's important to know what Unsafe Rust is. 不安全的程式碼通常都很簡短、受到隔離，而且封裝在安全的抽象層中。您應該仔細記錄這類程式碼的正 mut s = String::from("careful!"); let r1 = &mut s as *mut String; let r2 = r1 as *const String; // Safe because r1 and r2 were obtained from references and so are // guaranteed to be non-null and properly { println!("r1 is: {}", *r1); *r1 = String::from("uhoh"); println!("r2 is: {}", *r2); } // NOT SAFE. DO NOT DO THIS. /* let r3: &String = unsafe { &*r1 }; drop(s); println!("r3 is: {}", *r3); */ }

Task Migration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 330 25.9 Safe use of Finalizers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 331 26 Multi-processing since convert can be called implicitly, its methods are restricted to cases that are considered "safe" or "unsurprising". convert will only convert between types that repre- sent the same basic kind Finally, it takes account of changes in any compile-time preferences. If you know that a module is not safe to precompile (for example, for one of the reasons described below), you should put __precompile__(false)

Task Migration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 330 25.9 Safe use of Finalizers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 331 26 Multi-processing since convert can be called implicitly, its methods are restricted to cases that are considered "safe" or "unsurprising". convert will only convert between types that repre- sent the same basic kind Finally, it takes account of changes in any compile-time preferences. If you know that a module is not safe to precompile (for example, for one of the reasons described below), you should put __precompile__(false)

Task Migration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 330 25.9 Safe use of Finalizers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 331 26 Multi-processing since convert can be called implicitly, its methods are restricted to cases that are considered "safe" or "unsurprising". convert will only convert between types that repre- sent the same basic kind Finally, it takes account of changes in any compile-time preferences. If you know that a module is not safe to precompile (for example, for one of the reasons described below), you should put __precompile__(false)

Task Migration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 330 25.9 Safe use of Finalizers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 331 26 Multi-processing since convert can be called implicitly, its methods are restricted to cases that are considered "safe" or "unsurprising". convert will only convert between types that repre- sent the same basic kind Finally, it takes account of changes in any compile-time preferences. If you know that a module is not safe to precompile (for example, for one of the reasons described below), you should put __precompile__(false)

Task Migration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 308 24.11 Safe use of Finalizers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 308 25 Multi-processing since convert can be called implicitly, its methods are restricted to cases that are considered "safe" or "unsurprising". convert will only convert between types that repre- sent the same basic kind Finally, it takes account of changes in any compile-time preferences. If you know that a module is not safe to precompile (for example, for one of the reasons described below), you should put __precompile__(false)

Task Migration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 327 25.9 Safe use of Finalizers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 327 26 Multi-processing since convert can be called implicitly, its methods are restricted to cases that are considered "safe" or "unsurprising". convert will only convert between types that repre- sent the same basic kind Finally, it takes account of changes in any compile-time preferences. If you know that a module is not safe to precompile (for example, for one of the reasons described below), you should put __precompile__(false)

Task Migration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 330 25.9 Safe use of Finalizers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 331 26 Multi-processing since convert can be called implicitly, its methods are restricted to cases that are considered "safe" or "unsurprising". convert will only convert between types that repre- sent the same basic kind Finally, it takes account of changes in any compile-time preferences. If you know that a module is not safe to precompile (for example, for one of the reasons described below), you should put __precompile__(false)

Task Migration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 308 24.11 Safe use of Finalizers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 308 25 Multi-processing since convert can be called implicitly, its methods are restricted to cases that are considered "safe" or "unsurprising". convert will only convert between types that repre- sent the same basic kind Finally, it takes account of changes in any compile-time preferences. If you know that a module is not safe to precompile (for example, for one of the reasons described below), you should put __precompile__(false)

Task Migration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 327 25.9 Safe use of Finalizers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 327 26 Multi-processing since convert can be called implicitly, its methods are restricted to cases that are considered "safe" or "unsurprising". convert will only convert between types that repre- sent the same basic kind Finally, it takes account of changes in any compile-time preferences. If you know that a module is not safe to precompile (for example, for one of the reasons described below), you should put __precompile__(false)