How do I call a function that requires a 'static lifetime with a variable created in main?

Question

I\'ve got a struct defined that has a function which defines a static lifetime:

impl MyStruct {
    pub fn doSomething(&\'static self) {
        // Some          


        

Answer 1

The primary way to create a reference that has the 'static lifetime is to make the variable static. A static variable is one that can be created at compile time:

struct MyStruct;

impl MyStruct {
    pub fn do_something(&'static self) {}
}

static OBJ: MyStruct = MyStruct;

fn main() {
    OBJ.do_something();
}

As Rust's constant evaluation story improves, this will be more common, but it will never allow configuration at runtime.

A far less common method is to deliberately leak memory, producing a reference that will last "forever". This should be discouraged because leaking memory isn't a good thing:

fn main() {
    let obj = Box::leak(Box::new(MyStruct));
    obj.do_something();
}

There's also the possibility of creating a singleton:

• How do I create a global, mutable singleton?
• How can you make a safe static singleton in Rust?

as once main is complete the application should exit.

Perhaps, but the compiler doesn't treat main specially for lifetime purposes.

---

hyper requires a static runtime when running the server and processing each request.

No, it doesn't. It has a bound of : 'static, which means that any references passed in must be 'static, but you don't have to pass in a bare reference at all.

For patterns like this, the most common thing is to pass in something like an Arc. This allows sharing of the underlying resource.

pub fn do_something<F, T>(f: F)
where
    F: Fn() -> T + 'static,
    T: 'static,
{
    // "spawn" 3 threads
    f();
    f();
    f();
}

struct MyStruct;

static OBJ: MyStruct = MyStruct;

fn main() {
    // OK
    do_something(|| &OBJ);

    // Not OK
    let another = MyStruct;
    do_something(|| &another);

    // OK
    use std::sync::Arc;
    let shared = Arc::new(MyStruct);
    do_something(move || shared.clone());
}

You can even use interior mutability if you wanted dynamic reconfiguration.

See also:

• How do I use static lifetimes with threads?

Answer 2

The naive way to do this is with a static variable, but it will require unsafe code if you need to actually set the value inside your main function:

static mut OBJ: MyStruct = MyStruct;

fn main() {
    unsafe {
        OBJ = MyStruct {};
        OBJ.doSomething();
    }
}

It's also unsafe to do pretty much anything with a mutable static thereafter.

The much better way to do it is to let a library (lazy_static) take care of the unsafe code.

#[macro_use]
extern crate lazy_static;

fn main() {
    lazy_static!{
        static ref OBJ: MyStruct = MyStruct {};
    }
    OBJ.doSomething();
}