一般来讲，变量的析构顺序和声明顺序相反，但是并不是所有的情况都是这样。
本地变量
本地变量先声明后析构。
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| struct PrintDrop(&'static str);
impl Drop for PrintDrop {
fn drop(&mut self) {
println!("Dropping {}", self.0)
}
}
fn main() {
let _x = PrintDrop("x");
let _y = PrintDrop("y");
}
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| Dropping y
Dropping x
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元组
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| struct PrintDrop(&'static str);
impl Drop for PrintDrop {
fn drop(&mut self) {
println!("Dropping {}", self.0)
}
}
fn main() {
let _tup1 = (PrintDrop("x"), PrintDrop("y"));
let _tup2 = (PrintDrop("s"), PrintDrop("z"));
}
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| Dropping s
Dropping z
Dropping x
Dropping y
|
先析构 tup2 ，后析构 tup1 ，在元组内部是前面的先析构，后面的后析构。
结构体和枚举体
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| struct PrintDrop(&'static str);
impl Drop for PrintDrop {
fn drop(&mut self) {
println!("Dropping {}", self.0)
}
}
enum E {
Foo(PrintDrop, PrintDrop),
}
struct Foo {
_x: PrintDrop,
_y: PrintDrop,
_z: PrintDrop,
}
fn main() {
let _e = E::Foo(PrintDrop("a"), PrintDrop("b"));
let _f = Foo {
_x: PrintDrop("x"),
_y: PrintDrop("y"),
_z: PrintDrop("z"),
};
}
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| Dropping x
Dropping y
Dropping z
Dropping a
Dropping b
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闭包捕获变量
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| struct PrintDrop(&'static str);
impl Drop for PrintDrop {
fn drop(&mut self) {
println!("Dropping {}", self.0)
}
}
fn main() {
let z = PrintDrop("z");
let x = PrintDrop("x");
let y = PrintDrop("y");
let _closure = move || {
drop(y);
drop(z);
drop(x);
};
}
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| Dropping y
Dropping z
Dropping x
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闭包内的析构与捕获顺序相同，先捕获的先析构。