You need to specify a specific implementation of the trait in order to call the method.

Erroneous code example:

trait Coroutine {
    fn create() -> u32;
}

struct Impl;

impl Coroutine for Impl {
    fn create() -> u32 { 1 }
}

struct AnotherImpl;

impl Coroutine for AnotherImpl {
    fn create() -> u32 { 2 }
}

let cont: u32 = Coroutine::create();
// error, impossible to choose one of Coroutine trait implementation
// Should it be Impl or AnotherImpl, maybe something else?

This error can be solved by adding type annotations that provide the missing information to the compiler. In this case, the solution is to use a concrete type:

trait Coroutine {
    fn create() -> u32;
}

struct AnotherImpl;

impl Coroutine for AnotherImpl {
    fn create() -> u32 { 2 }
}

let gen1 = AnotherImpl::create();

// if there are multiple methods with same name (different traits)
let gen2 = <AnotherImpl as Coroutine>::create();