生锈多生寿命结构可以访问超出寿命更长的参数
struct TwoStrRef<'a, 'b> {
str1: &'a str,
str2: &'b str,
}
fn main() {
let a_ref_struct;
let string_1 = String::from("hello");
let str_ref;
{
let string_2 = String::from("world");
a_ref_struct = TwoStrRef {
str1: &string_1,
str2: &string_2,
};
str_ref = a_ref_struct.str1;
}
// str_ref; // Ok
// a_ref_struct.str1; // Error: `string_2` does not live long enough borrowed value does not live long enough
}
struct twostrref， a'和'b有两个寿命参数，我分配了string_1的参考String_2（在不同的范围中，String_1是一个较长的范围），str_1和str_2，以及当我尝试访问A_REF_STRUCT.STR1 String_2之外（但是与String_1）相同时，编译器将丢弃错误，这指示已指示。 String_2寿命不够长。 str1字段是否保存不在其范围之外的String_1的引用？为什么如果我将STR1引用分配给str_ref，我可以在同一范围内使用String_1访问它？
struct TwoStrRef<'a, 'b> {
str1: &'a str,
str2: &'b str,
}
fn main() {
let a_ref_struct;
let string_1 = String::from("hello");
let str_ref;
{
let string_2 = String::from("world");
a_ref_struct = TwoStrRef {
str1: &string_1,
str2: &string_2,
};
str_ref = a_ref_struct.str1;
}
// str_ref; // Ok
// a_ref_struct.str1; // Error: `string_2` does not live long enough borrowed value does not live long enough
}
there are two lifetime parameters for struct TwoStrRef, a' and 'b, and I assign the reference of string_1 and string_2 (which are in different scope and string_1 is the longer one) to field str_1 and str_2, and when I try to access a_ref_struct.str1 outside the scope of string_2 (but the same with string_1), the compiler will throw error, which indicated that string_2 does not live long enough. Isn't the str1 field holds the reference of string_1 that is not outside its scope ? And why if I assign the str1 reference to str_ref, I can access it in the same scope with string_1?
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A_REF_STRUCT在string_2之前删除 脱离范围：这是必需的，因为否则任何访问其str2field> field（例如，它可能在其滴剂处理程序中发生）是无效的。实际上，如果a_ref_struct在删除string2之后，其str2将成为已发布的内存中的参考从未访问。在那里，您只是在
a_ref_struct.str1（使用lifetime'aofstring_1）中存储并存储该副本进入str_ref。A_REF_STRUCT可以（并且被）删除而不会影响（复制）参考。a_ref_structis dropped beforestring_2goes out of scope: this is required because otherwise any access of itsstr2field (which could potentially occur in its drop handler, for example) would be invalid. Indeed ifa_ref_structwere to exist afterstring2is dropped, itsstr2would be a reference into released memory which is Undefined Behaviour even if that reference is never accessed.There you are just taking a copy of the reference that is held in
a_ref_struct.str1(with lifetime'aofstring_1) and storing that copy intostr_ref.a_ref_structcan then be (and is) dropped without affecting that (copied) reference.