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Обсуждение на тему: Rust static

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Rust static

On the surface, static items seem very similar to consts both contain a value, both require type annotations and both can only be initialized with constant functions and values. However, statics are notably different in that they represent a location in memory. That means that you can have references to static items and potentially even modify them, making them essentially global variables. A static item is similar to a constant, except that it represents a precise memory location in the program. Static items have the static lifetime, which outlives all other lifetimes in a rust program. The initializer expression must be omitted in an external block, and must be provided for free static items.

Вы можете столкнуться с ним в двух случаях !allow(unused) fn main() ссылка с временем жизни static let s &static str hello world static как часть ограничения типажа fn generict(x t) where t static . Оба они похожи, но немного отличаются, что часто вызывает путаницу при изучении rust. Rust имеет одну специальную встроенную аннотацию, которая называется static и которая означает, что ссылка будет существовать в течение всей программы. The same default that rfc 599 sets up for trait object is to be used for statics and const declarations. In those declarations, the compiler will assume static when a lifetime is not explicitly given in all reference lifetimes, including reference lifetimes obtained via generic substitution. Note that this rfc does not forbid writing the lifetimes, it only sets a default when no is given.

Thus the change will not cause any breakage and is therefore backwards-compatible. Their initial value is const-evaluated at compile time and has a static lifetime. A static variable can be declared within a function, which makes it inaccessible outside of the function however, this doesnt affect its lifetime (it isnt dropped at the end of the function). This means that their type must implement the sync this links to official rust documentation trait. Statics will have a dedicated section in your binary where they will be placed (the bss section, see where are static variables stored in c and c? For further information). When not possible, because you need to initialize a variable later in the program of with non-const methods, use lazystatic.

While both const and static can use interior mutability you should never ever do it with a const. Use stdsyncatomicatomicu32, ordering but it can still be coerced to a shorter lifetime. There are several ways to make a variable with static lifetime, two of them are stored in the read-only memory of the binary. Fill in the blank in two ways fn main() needstatic(v) println!(success!) fn needstatic(r &static str) asserteq!(r, hello) another way to make static lifetime is using boxleak. Derive(debug) struct config a string, b string, static mut config option&mut config none используя правила вывода времён жизни, rust автоматически выводит ограничение static в первой функции, поэтому у них обеих фактически есть ограничение static. .